Newsletter No. 81 October 2019

GANEX III-N Technology

Coordinated by CRHEA-CNRS research laboratory, this monthly newsletter is produced by Knowmade with collaboration from the managers of GANEX groups. The newsletter presents a selection of newest scientific publications, patent applications and press releases related to III- Nitride semiconductor materials (GaN, AlN, InN and alloys)

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METHODOLOGY

Sources 10+ scientific journal editors Elsevier, IOP, IEEE, Wiley, Springer, APS, AIP, AVS, ECS, Nature, Science … 10+ specialist magazines Semiconductor Today, ElectoIQ, i-micronews, Compound Semiconductor, Solid State Technology … 5+ open access database: FreeFulPDF, DOAJ …

Patent database: Questel-Orbit

Each month 150+ new scientific publications 200+ new patent applications 30+ new press releases

Selection by III-N French experts

GANEX monthly newsletter

GaNEX | III-N Technology Newsletter No. 81 | 2

TABLE OF CONTENTS (clickable links to chapters)

SCIENTIFIC PUBLICATIONS ...... 4

GROUP 1 - LEDs and Lighting ...... 4

GROUP 2 - Laser and Coherent Light ...... 12

GROUP 3 - Power Electronics ...... 14

GROUP 4 - Advanced Electronics and RF ...... 23

GROUP 5 – MEMS and Sensors...... 29

GROUP 6 - Photovoltaics and Energy harvesting...... 34

GROUP 7 - Materials, Technology and Fundamental ...... 38

PRESS RELEASE ...... 51

PATENT APPLICATIONS ...... 75

GaNEX | III-N Technology Newsletter No. 81 | 3

SCIENTIFIC PUBLICATIONS Selection of new scientific articles

GROUP 1 - LEDs and Lighting Group leader: Benjamin Damilano (CRHEA-CNRS) Information selected by Benjamin Damilano and Mathieu Leroux (CRHEA-CNRS)

Size-independent peak efficiency of III-nitride micro- demonstrate localized-surface-plasmon (LSP)- light-emitting-diodes using chemical treatment and enhanced GaN:Eu-based red LEDs utilizing Ag sidewall passivation nanoparticles (NPs) as one of the approaches to Materials Department, University of California, Santa enhance the output power. Size-controllable NPs are Barbara, CA, 93106, United States of America formed by Ag deposition on the GaN:Eu followed by Department of Electrical and Computer Engineering, thermal annealing. The photoluminescence intensity University of California, Santa Barbara, CA, 93106, United of the GaN:Eu LEDs with the NPs increases by 340% States of America compared to those without the NPs. A shorter

emission lifetime of the LEDs with the NPs Applied Physics Express https://doi.org/10.7567/1882-0786/ab3949 demonstrates the coupling of Eu3+ ions to the LSPs. Furthermore, the LEDs with the NPs show an Micro-light-emitting-diodes (μLEDs) with size- enhancement of the output power of 210% under independent peak external quantum efficiency current injection due to LSP coupling. behavior was demonstrated from 10 × 10 μm2 to 100 × 100 μm2 by employing a combination of chemical Influence of substrate off-cut angle on the treatment and atomic-layer deposition (ALD) sidewall performance of 310 nm light emitting diodes passivation. The chemical treatment and sidewall Ferdinand-Braun-Institut, Leibniz-Institut für passivation improved the ideality factors of μLEDs Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany from 3.4 to 2.5. The results from the combination of UVphotonics NT GmbH, Gustav-Kirchhoff-Straße 4, 12489 chemical treatment and ALD sidewall passivation Berlin, Germany suggest the issue of size dependent efficiency can be Technische Universität Berlin, Institute of Solid State resolved with proper sidewall treatments after dry Physics, Hardenbergstraße 36, 10623 Berlin, Germany etching. Humboldt University of Berlin, Institute of Physics, Newtonstraße 15, 12489 Berlin, Germany Localized-surface-plasmon-enhanced GaN:Eu-based red light-emitting diodes utilizing silver Journal of Crystal Growth nanoparticles https://doi.org/10.1016/j.jcrysgro.2019.125241 Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, The influence of the sapphire substrate off-cut angle Suita, Osaka 565-0871, Japan from c-plane orientation on the surface morphology of AlN/AlGaN layers and the performance of 310 nm Applied Physics Express light emitting diode structures has been investigated. https://doi.org/10.7567/1882-0786/ab37b0 Increasing the off-cut angle from 0.1° to 10° towards the m-plane leads to a change of the (Al,Ga)N growth GaN:Eu-based red light-emitting diodes (LEDs), mode, threading dislocation density, and emission characterized by spectrally stable and narrow- characteristics of ultraviolet light emitting diodes wavelength operation, have recently reached output- (LEDs). The growth mode changed from step-flow powers respectable for commercialization. Further with bilayer steps to step-bunching and finally to enhancement of Eu3+ luminescence is currently rough 3D growth. The lowest threading dislocation being pursued in order to facilitate their density has been observed for structures deposited implementation into next-generation applications, on sapphire with an off-cut angle of 0.65°, whereas such as micro-LED displays. In this letter, we the emission power is the highest for structures

GaNEX | III-N Technology Newsletter No. 81 | 4 grown on substrates with an off-cut of 0.48°. On-chip GaN-based dual-color micro-LED arrays and Electroluminescence measurements display single their application in visible light communication peaks for structures on substrates with off-cut angles Institute of Photonics, Department of Physics, University of of up to 0.65°. The emission peak full width at half Strathclyde, Glasgow G1 1RD, UK maximum remains nearly constant (∼ 9.5 nm) for Institute for Digital Communications, Li–Fi R&D Centre, structures with off-cut angels up to 0.21° and University of Edinburgh, Edinburgh EH9 3JL, UK increases to 11.7 nm and 21.0 nm for 0.48° and 0.65°, Optics Express respectively. The emission wavelength is almost https://doi.org/10.1364/OE.27.0A1517 unchanged by the use of off-cut angles up to 0.48° (311 nm) and increases to 319 nm for 0.65°. Larger Integrated multi-color micron-sized light emitting off-cut angles cause multiple emission peaks diode (micro-LED) arrays have been demonstrated in indicating compositional inhomogeneity of the recent years for display applications; however, their InAlGaN quantum wells. potential as visible light communication (VLC) transmitters is yet to be fully explored. In this work, Enhanced performance of vertical-structured InGaN we report on the fabrication and characterization of micro-pixelated light-emitting-diode array on-chip dual-color micro-LED arrays and their fabricated using an ion implantation process application in VLC. For this purpose, blue-green and Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese blue-violet micro-LED arrays were fabricated by Academy of Sciences, Suzhou 215100, China transfer printing blue-emitting micro-LEDs onto the Institute of Opto-Electronic NJU&Yangzhou, Yangzhou 225009, China substrate of green and violet micro-LEDs, respectively. The potential of these dual-color micro- Optics Letters LED arrays as VLC transmitters is demonstrated with https://doi.org/10.1364/OL.44.004562 respective error-free data rates of 1.79 and 3.35 Gbps, achieved by the blue-green and blue-violet In this Letter, a new approach to fabricating a high- devices in a dual wavelength multiplexing scheme. efficiency vertical-structured InGaN micro-pixelated light-emitting diode (μVLED) is presented. The high- Optical polarization characteristics and light resistivity selective areas are intentionally created in extraction behavior of deep-ultraviolet LED flip-chip the n-GaN layer through a fluorine (F) ion- with full-spatial omnidirectional reflector system implantation process and then used as the electrical Wuhan National Laboratory for Optoelectronics, Huazhong isolation regions for realizing a μVLED array University of Science and Technology, Luoyu Road 1037, consisting of 25×25 pixels with a diameter of 10 μm. Wuhan 430074, China The results prove that the dual-energy F− ion Optics Express implantations not only can improve the uniformity of https://doi.org/10.1364/OE.27.0A1601 carrier distribution but also can effectively prevent current from leaking along the etched sidewalls, Optical polarization characteristics and light which in turn realize a more efficient carrier injection extraction behavior of deep-ultraviolet (DUV) light- into the mesa area. More notably, the current- emitting diode (LED) flip-chip with full-spatial handling capability and corresponding optical output omnidirectional reflector (FSODR) have been power density of the μVLED array are substantially investigated. FSODR is fabricated to be higher than those of conventional vertical-structured simultaneously covered on the whole flip-chip, broad-area LEDs. A measured output light power except the sapphire surface. It is found that the density of the F− ion-implanted μVLED array reaches FSODR greatly enhance both transverse-electric (TE) a maximum value of 43 W cm−2 at 3.06 kA cm−2, and transverse-magnetic (TM) mode light extraction before power saturation. The improved luminescence at every space angle, resulting in total enhancement performances of the μVLED array can be attributed to of 73.1% and 79.8%, respectively. Moreover, the four an effective ion-induced heat relaxation and individual ODR structures separated from FSODR, associated lower junction temperature. which are covered on the surface of n-AlGaN, the

GaNEX | III-N Technology Newsletter No. 81 | 5 interface of p-GaN/p-AlGaN, the sidewall of mesa and Characteristics of Micro LEDs With Snowflake p- the sidewall of n-AlGaN/AlN, respectively, show Electrode and Composite Textured Sidewalls considerably different optical polarization Engineering Research Center for Optoelectronics of characteristics and extraction behaviors between Guangdong Province, School of Electronic and Information each other. The achievements of FSODR cannot be Engineering, South China University of Technology, obtained by any separated ODR, and all of the Guangzhou 510640, China Zhongshan Institute of Modern Industrial Technology, individual ODRs can contribute to the FSODR. South China University of Technology, Zhongshan 528437, Especially, the synergy effect of TM extraction China behavior obviously exists in FSODR. As a result, the light extraction efficiency (LEE) enhancement of IEEE Photonics Technology Letters FSODR is approximately 60% at a high current density https://doi.org/10.1109/LPT.2019.2942690 of 140A/cm2. This study is significant for understanding and modulating the extraction We demonstrate a hybrid structure incorporating behavior of polarized light to realize high efficiency concave-convex circular composite textured sidewalls AlGaN-based DUV LEDs. and snowflake-like p-electrode, which is an effective approach to improve optical properties without Stability and degradation of AlGaN-based UV-B deteriorating the electrical characteristics for micro- LEDs: Role of doping and semiconductor defects LEDs. Compared to the device with flat sidewalls and Department of Information Engineering, University of disk p-electrode, the device with concave-convex Padova, via Gradenigo 6/B, Padova 35131, Italy circular composite textured sidewalls and 6-branches Institute of Materials and Systems for Sustainability snowflake-like p-electrode exhibits a saturation light (IMaSS), Nagoya University, Nagoya 464-8601, Japan output power enhancement of 36.85%. And the Nikkiso Giken Co., Ltd., 1-5-1 Asahigaoka, Hakusan, forward voltage decreases by 7.6% at current density Ishikawa 924-0004, Japan of 1732.4 A/cm2. The enhanced performances are Microelectronics Reliability mainly attributed to the decrease of total internal https://doi.org/10.1016/j.microrel.2019.113418 reflection at the concave-convex circular composite textured sidewalls and improvement of current Within this paper, we present an extensive analysis of distribution provided by 6-branches snowflake-like p- the degradation of UV-B light-emitting diodes (LEDs) electrode. submitted to constant current stress. The study is based on combined electrical, optical and spectral Observation and modeling of leakage current in characterization, and capacitance deep-level AlGaN ultraviolet light emitting diodes transient spectroscopy (C-DLTS). The results of this Jiangsu Provincial Key Laboratory of Advanced Photonic analysis demonstrate that the decrease in the optical and Electronic Materials, School of Electronic Science and power during the stress is stronger at low measuring Engineering, Nanjing National Laboratory of Microstructures, Nanjing University current levels, indicating that the degradation is College of Electronic and Optical Engineering & College of related to the increase in Shockley-Read-Hall (SRH) Microelectronics, Nanjing University of Posts and recombination. The electrical characterization shows Telecommunications, Xiamen University a decrease in the driving voltage, probably due to an increased activation of the Mg dopant, and an IEEE Photonics Technology Letters increase in the sub-threshold forward current, that https://doi.org/10.1109/LPT.2019.2942612 suggest a generation of mid-gap states during the stress. C-DLTS measurements were carried out to Current-voltage (I-V) characteristics of AlGaN study the variation in defects concentration after ultraviolet light-emitting diodes (UV-LEDs) under the stress; the most relevant traps were ascribed to the temperatures ranging from 50 K to 300 K are presence of Mg doping and/or to intrinsic defects analyzed. The abnormal diode characteristics of UV- related to the GaN growth. LEDs below the turn-on voltage indicate the existence of space-charge-limited (SCL) current transport in the presence of deep trap states, which induce a non- GaNEX | III-N Technology Newsletter No. 81 | 6 linear current leakage effect. The SCL current is Effects of InAlN underlayer on deep traps detected gradually overwhelmed by Ohmic leakage as the in near-UV InGaN/GaN single quantum well light- temperature increases, which is mainly due to the emitting diodes thermally generated carrier concentration and traps National University of Science and Technology MISiS, deactivation. A modified three-diode circuit model is Moscow 119049, Russia suggested with an additional series resistor and diode Institute of Physics, Ecole Polytechnique Fédérale de to emulate the forward-bias I-V characteristics of UV- Lausanne (EPFL), CH-1015 Lausanne, Switzerland Laboratory of Radiation Technologies, A. N. Frumkin LEDs. An excellent fit to the I-V curves of UV-LEDs is Institute of Physical Chemistry and Electrochemistry achieved, which illustrates the impact of deep trap Russian Academy of Sciences (IPCE RAS), Moscow 119071, states on the electrical characteristics of UV-LEDs. Russia Department of Engineering, University of Palermo, I- Monolithically Integrated GaN LED/Quasi-Vertical 90128, Palermo, Italy Power U-shaped Trench-gate MOSFET Pairs using Department of Materials Science and Engineering, Selective Epi Removal University of Florida, Gainesville, Florida 32611, USA Rensselaer Polytechnic Institute, Troy, NY 12180, USA Taiyo Nippon Sanso Corporation, Tsukuba, Ibaraki 300- Journal of Applied Physics 2611, Japan https://doi.org/10.1063/1.5122314 MATHESON Tri-Gas, 150 Allen Road, Suite 302, Basking Ridge, NJ 07920, USA Two types of near-UV light-emitting diodes (LEDs) with an InGaN/GaN single quantum well (QW) IEEE Electron Device Letters differing only in the presence or absence of an https://doi.org/10.1109/LED.2019.2943911 underlayer (UL) consisting of an InAlN/GaN

superlattice (SL) were examined. The InAlN-based ULs We report on the demonstration of monolithically were previously shown to dramatically improve integrated light-emitting diode (LED) and quasi- internal quantum efficiency of near-UV LEDs, via a vertical U-shaped trench-gate metal-oxide- decrease in the density of deep traps responsible for semiconductor field-effect transistor (UMOSFET) in nonradiative recombination in the QW region. The GaN. Selective epi removal (SER) approach was used main differences between samples with and without on an LED-on-FET epi stack on sapphire substrates. UL were (a) a higher compensation of Mg acceptors Individual p-GaN layers were used for LED and FET in in the p-GaN:Mg contact layer of the sample without our design. LED light modulation by the supply UL, which correlates with the presence of traps with voltage and the FET gate voltage was realized, and an an activation energy of 0.06 eV in the QW region, (b) integrated 350μm× 350μm LED/UMOSFET pair the presence of deep electron traps with levels 0.6 eV exhibits a light output power (LOP) of 4.9 W/cm2 or below the conduction band edge (Ec) (ET1) and at Ec 6.0 mW. An integrated device with a UMOSFET 0.77 eV (ET2) in the n-GaN spacer underneath the driving a 3-LED chain was also demonstrated. The QW, and the presence of hole traps (HT1) in the QW, normally-off power UMOSFET has a threshold voltage 0.73 eV above the valence band edge in the sample of 7 V, a breakdown voltage of 208 V, and a specific without UL (no traps could be detected in the sample on-resistance of 23 mμ-cm2, in which hexagonal cells with UL), and (c) a high density of deep traps with were applied to obtain identical m-plane MOS gate optical ionization energy close to 1.5 eV for the LEDs interfaces. The effect of FET sizing on integrated pairs without UL. Irradiation with 5 MeV electrons led to a was also studied, and a trade-off model of FET/LED strong decrease in the electroluminescence (EL) power ratio vs. FET/LED area ratio was created, which intensity in the LEDs without UL, while for the serves as universal criterion for FET/LED integration. samples with UL, such irradiation had little effect on The tested device with the best trade-off has FET/LED the EL signal at high driving current, although the area ratio of 24% and FET/LED power ratio of 56%. level of driving currents necessary to have a This work creates a new building block for future GaN measurable EL signal increased by about an order of light-emitting integrated circuits (LEICs). magnitude. This is despite the 5 times higher starting

EL signal of the sample with UL. Irradiation also led to

GaNEX | III-N Technology Newsletter No. 81 | 7 the appearance in the LEDs with UL of the ET1 and Room-temperature stability of excitons and HT1 deep traps, but with concentration much lower transverse-electric polarized deep-ultraviolet than without the UL, and to a considerable increase luminescence in atomically thin GaN quantum wells in the Mg compensation ratio. Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA Compositional accuracy in atom probe tomography analyses performed on III-N light emitting diodes Applied Physics Letters https://doi.org/10.1063/1.5111546 UNIROUEN, INSA Rouen, CNRS, Groupe de Physique des

Matériaux, Normandie Université, 76000 Rouen, France CEMES-CNRS, 29 rue Jeanne Marvig, Toulouse, France We apply first-principles calculations to study the Ioffe Institute, 194021 St. Petersburg, Russia effects of extreme quantum confinement on the Submicron Heterostructures for Microelectronics Research electronic, excitonic, and radiative properties of and Engineering Center RAS, 194021 St. Petersburg, Russia atomically thin (1–4 atomic monolayers) GaN Materials Department, University of California, Santa quantum wells embedded in AlN. We determine the Barbara, California 93106, USA quasiparticle bandgaps, exciton energies and wave functions, radiative lifetimes, and Mott critical Journal of Applied Physics densities as a function of well and barrier thickness. https://doi.org/10.1063/1.5113799 Our results show that quantum confinement in GaN

monolayers increases the bandgap up to 5.44 eV and Laser-assisted atom probe tomography (APT) and the exciton binding energy up to 215 meV, indicating high-resolution dark-field electron holography (HR- the thermal stability of excitons at room DFEH) were performed to investigate the temperature. Exciton radiative lifetimes range from 1 composition of a polar [0001] to 3 ns at room temperature, while the Mott critical GaN/AlxGa1 − xN/InyGa1 − yN light emitting diode. In density for exciton dissociation is approximately particular, the III-site fraction of both AlxGa1 − xN 1013 cm−2. The luminescence is transverse-electric and InyGa1 − yN alloys was studied adopting a polarized, which facilitates light extraction from c- comparative approach. HR-DFEH allows mapping the plane heterostructures. We also introduce a simple projected strain with a subnanometer spatial approximate model for calculating the exciton resolution which is used for the calculation of the radiative lifetime based on the free-carrier two-dimensional alloy composition distribution. APT bimolecular radiative recombination coefficient and provides three-dimensional alloys composition the exciton radius, which agrees well with our results distribution with a nanometer spatial resolution. obtained with the Bethe–Salpeter equation However, here we reveal that important inaccuracies predictions. Our results demonstrate that atomically affect local composition measurements. A Ga-poor thin GaN quantum wells exhibit stable excitons at composition is obtained in high DC-electric field room temperature for potential applications in regions. Moreover, such inaccuracies may be locally efficient light emitters in the deep ultraviolet as well enhanced where the [0001] pole intersects the as room-temperature excitonic devices. surface of the analyzed specimen, leading to a lower fraction of Ga measured. III-site fractions closer to Recombination pathways and hole leakage behavior the nominal values were measured at low field in InGaN/GaN multiple quantum wells with V- conditions. Ga loss is thought to be due to shaped pits preferential DC field induced evaporation of Ga ions National Institute of LED on Si Substrate, Nanchang between laser pulses. This is explained in terms of University, Nanchang, 330096, China formation of a metallic layer on the tip surface during APT analysis, where weak Ga-Ga bonds are formed, Superlattices and Microstructures promoting the loss of Ga at high field conditions. https://doi.org/10.1016/j.spmi.2019.106284

Hole transport in InGaN/GaN multiple quantum wells (MQWs) LEDs has been proposed to be insufficient due to relatively large effective mass and low GaNEX | III-N Technology Newsletter No. 81 | 8 mobility. Here, for the first time, we have direct alternating AlN thin films using an explicit observed hole overflow from MQWs and enter into combination of low-n and high-n to further InGaN/GaN superlattices (SLs) layer in V-pits- investigate the thin film optical properties. The effect containing GaN-based green LEDs at room of structural transformation in the DBR stack on the temperature. To suppress the hole leakage, an n- progress of optical properties was studied. The DBRs AlGaN hole blocking layer (HBL) is inserted between exhibit a negligible extinction coefficient, utilizing SLs layer and MQWs. The experimental show an precise control of oxygen incorporation with one interesting and baffling result is that the HBL- sputtering target. containing sample not only exhibits severe hole leakage in high current density range, but also has High-power and reliable GaN-based vertical light- higher external quantum efficiency (EQE). Numerical emitting diodes on 4-inch silicon substrate simulation reveals that the HBL can change the Key Laboratory of Hydraulic Machinery Transients (Wuhan transportation path of carriers, forcing more University), Ministry of Education, Wuhan 430072, China electrons injecting from c-plane into the MQWs Center for Photonics and Semiconductors, School of Power instead of from V-pit sidewalls. This will increase the and Mechanical Engineering, Wuhan University, Wuhan 430072, China carrier concentration in the MQWs, and eventually State Key Laboratory of Applied Optics, Changchun lead to higher EQE. Meanwhile, less electrons Institute of Optics, Fine Mechanics and Physics, Chinese transported through V-pit allowed more holes Academy of Sciences, Changchun 130033, China injecting into deeper layers via V-pit sidewalls, and Xiamen Changelight Co. Ltd., Xiamen 361000, China electroluminescence emission from the SLs layer became stronger when HBL was inserted. Optics Express https://doi.org/10.1364/OE.27.0A1506 Study of optical and structural properties of sputtered aluminum nitride films with controlled High-power and reliable GaN-based vertical light- oxygen content to fabricate Distributed Bragg emitting diodes (V-LEDs) on 4-inch silicon substrate Reflectors for ultraviolet A were fabricated and characterized in this article. The GC University Lahore, Department of Physics, Kachary metallization scheme reliability was improved by Road, Lahore, 54000, Pakistan depositing the Pt/Ti films that surround the Nanostructured Energy Conversion Technology and compressed Ag/TiW films to protect it from Research (NECTAR), University of California Santa Cruz, environmental humidity. We demonstrated that Santa Cruz, CA, 95064, USA although current crowding in V-LEDs was not as NanoLab Technologies, Inc., Milpitas, CA, 95035, USA severe as that in lateral light-emitting diodes (L-LEDs), Foothill College, Los Alto Hills, CA, 94022, USA high current density around the opaque metal n-

electrode in V-LEDs remained a problem. A SiO2 Optical Materials https://doi.org/10.1016/j.optmat.2019.109405 current blocking layer (CBL) was incorporated in V- LEDs to modify the current distribution. Roughening Aluminum nitride (AlN) films with controlled oxygen the emitting surface of V-LEDs with KOH and H3PO4 content were deposited on silicon substrates, and etchant was compared and the influence of surface optical properties studied with dependency on film roughening on the emission property of V-LEDs was morphology. Combinations of argon (Ar) and nitrogen studied. The high-power V-LEDs showed low forward (N2) gases were used in RF magnetron sputtering of voltage with small series resistance and high light an AlN target. The resulting refractive index ranging output power (LOP) without saturation up to 1300 from 1.6 to 2.0 at 400 nm was tuned by controlling mA. Under 350 mA injection current, V-LEDs achieved the sputter gas flow rate ratio of Ar and N2. The an excellent light output power (LOP) of 501 mW resulting refractive index is associated with density with the peak emission wavelength at 453 nm. The and aluminum nitride content of the thin films. prominent output performance of V-LEDs Distributed Bragg Reflectors (DBRs) optimized for demonstrated in this work confirmed that integrating ultraviolet-A reflectivity were fabricated with pairs of the optimized metallization scheme, SiO2 CBL and

GaNEX | III-N Technology Newsletter No. 81 | 9 surface texturing by KOH wet etching is an effective standard ABC model. With the increase of the approach to higher performance V-LEDs. polarization, effective volume decreases which causes strong localization of carriers at lower High-performance flat-type InGaN-based light- potentials causing the carrier density to increase. This emitting diodes with local breakdown conductive effect leads to loss mechanisms such as carrier channel leakage and Auger loss. Our theoretical analysis for Department of Nano-Optical Engineering, Korea internal quantum efficiency and light output power Polytechnic University, Siheung, 15073, Republic of Korea shows good agreement with the experimental results for both the blue and green InGaN light-emitting Scientific Reports diodes. https://doi.org/10.1038/s41598-019-49727-4

Flat-type InGaN-based light-emitting diodes (LEDs) Greatly enhanced performance of AlGaN-based without an n-type contact electrode were developed deep ultraviolet light emitting diodes by introducing by using a local breakdown conductive channel a polarization modulated electron blocking layer State Key Laboratory of Artificial Microstructure and (LBCC), and the effect of the In content of the InGaN Mesoscopic Physics, School of Physics, Peking University, quantum wells (QWs) on the local breakdown Beijing 100871, China phenomenon was investigated. Electroluminescence Nano-optoelectronics Frontier Center of Ministry of and X-ray analyses demonstrated that the Education, Peking University, Beijing 100871, China homogeneity and crystallinity of the InGaN QWs Collaborative Innovation Center of Quantum Matter, deteriorated as the In content of the InGaN QWs Beijing 100871, China increased, thereby increasing the reverse leakage current and decreasing the breakdown voltage. After Optics Express reverse breakdown with a reverse current of several https://doi.org/10.1364/OE.27.0A1458 mA, an LBCC was formed on the GaN-based LEDs. The surface size and anisotropic shape of the LBCC Carrier transport in AlGaN-based deep ultraviolet increased as the indium content of the InGaN QWs in (DUV) light emitting diodes (LEDs) with the the LEDs increased. Moreover, a flat-type InGaN LED wavelength of 273 nm has been investigated by without an n-type electrode was developed by using introducing polarization modulated electron blocking the LBCC. Notably, the resistance of the LBCC layer (EBL) that adopts an Al composition and decreased with increasing indium content in the thickness graded multiple quantum barriers (MQB) InGaN QWs, leading to lower resistance and higher structure. The experimental result shows that the light emission of the flat-type InGaN-based LEDs maximum light output power and external quantum without an n-type contact electrode. efficiency for the proposed structure at the current of 250 mA are 9.6 mW and 1.03% respectively, severally Analytical analysis of internal quantum efficiency increasing by 405% and 249% compared to with polarization fields in GaN-based light-emitting traditional one, meanwhile, the efficiency droop at diodes 250 mA is also dramatically reduced from 42.2% to Faculty of Engineering Sciences, Ghulam Ishaq Khan 16.6%. Further simulation analysis indicates that this Institute of Engineering Sciences and Technology, Topi, graded MQB-EBL enhances the potential barrier 23460, Khyber Pakhtunkhwa, Pakistan height for electrons and meanwhile reduces that for holes, hence effectively suppresses the electron Superlattices and Microstructures leakage, and at the same time significantly improves https://doi.org/10.1016/j.spmi.2019.106271 the hole injection efficiency. As a result, the whole performance of the LED with the proposed MQB-EBL This paper presents the analytical model for the is dramatically improved. analysis of internal quantum efficiency as well as light output power of GaN-based light-emitting diodes by introducing the polarization factor, which accounts for the polarization fields in the active region, in the

GaNEX | III-N Technology Newsletter No. 81 | 10

Advantages of AlGaN-based deep-ultraviolet light- QBs in conventional LEDs. As a result, the electron emitting diodes with an Al-composition graded and hole concentration in the active region was quantum barrier considerably increased, attributing to the success of School of Microelectronics, University of Science and the electron blocking effect and enhanced hole Technology of China, Hefei, Anhui 230026, China injection efficiency. Importantly, the optical power Jacobs School of Engineering, University of California San was remarkably improved by 65.83% at the injection Diego, La Jolla, CA 92093, USA current of 60 mA. After in-depth device optimization, Wuhan National Laboratory for Optoelectronics, Huazhong we found that a relatively thinner graded QB layer University of Science and Technology, Wuhan, 430074, could further boost the LED performance because of China the increased carrier concentrations and enhanced Optics Express electron and hole wave function overlap in the QW, https://doi.org/10.1364/OE.27.0A1544 triggering a much higher radiative recombination efficiency. Hence, the proposed graded QBs, which AlGaN-based deep-ultraviolet light-emitting diodes have a continuous increment of Al composition along (DUV LEDs) still suffer from poor quantum efficiency the growth direction, provide us with an effective and low optical power. In this work, we proposed a solution to boost light output power in the pursuit of DUV LED structure that includes five unique AlxGa1- high-performance DUV emitters. xN quantum barriers (QBs); Each QB has a linear- increment of Al composition by 0.03 along the growth direction, unlike those commonly used flat

GaNEX | III-N Technology Newsletter No. 81 | 11

GROUP 2 - Laser and Coherent Light Group leader: Bruno Gayral (CEA) Information selected by Knowmade

Watt-class blue vertical-cavity surface-emitting laser width at half maximum). This laser operation arrays demonstration for the GaN-based MC structure R&D Laboratories, Stanley Electric Co., Ltd., 1-3-1 Edanishi, employing an HCG exhibited the advantages of HCGs Aoba-ku, Yokohama 225-0014, Japan in semiconductor lasers at wavelengths from green to ultraviolet. Applied Physics Express https://doi.org/10.7567/1882-0786/ab3aa6 Critical analysis of step-graded polarisation

engineered electron-blocking layer optimisation for We have successfully demonstrated a high output InGaN MQW laser diode power of 1.19 W from a two-dimensional 16 × 16 Academy of Scientific and Innovative Research (AcSIR), blue GaN-based vertical-cavity surface-emitting laser CSIR-Central Electronics Engineering Research Institute (VCSEL) array under continuous wave operation at a (CSIR-CEERI) Campus, India lasing wavelength of 447 nm. A 256-element VCSEL Optoelectronics and MOEMS Group, CSIR-CEERI, India array exhibited a high-quality far-field beam pattern with a circular shape and narrow divergence angle of IET Optoelectronics around 7°. A very small shift of the lasing wavelength https://doi.org/10.1049/iet-opt.2018.5110 with a change in the dissipated power of 0.05 nm W−1 revealed a very low thermal resistance of 3.4 K Here, the authors have optimised electron-blocking W−1. layer (EBL) with step graded design for a laser diode (LD) with an emission wavelength of 450 nm. Step Demonstration of polarization control GaN-based graded EBL contain layers of varying compositions micro-cavity lasers using a rigid high-contrast grating from In 0.04 Ga 0.96 N to Al 0.2 Ga 0.8 N with the reflector total thickness of 30 nm. The electron leakage has Department of Photonics, College of Electrical and reduced from ~2272 to ~6.6 A cm -2, while hole Computer Engineering, National Chiao Tung University, transportation has improved by 2.185at 10 kA cm -2 Hsinchu, 30010, Taiwan injected current density. The light output power per facet of reference LD is 146.8 mW, which the authors Scientific Reports have enhanced to 247.7 mW in authors' step-graded https://doi.org/10.1038/s41598-019-49604-0 EBL structure. The slope efficiency has increased by

~61.9%. Also, the EBL energybarrier hasincreased by We reported on GaN microcavity (MC) lasers 324.2 meV, while the hole transportation barrierhas combined with one rigid TiO2 high-contrast grating reduced by 77.1 meV. The reduction in hole (HCG) structure as the output mirror. The HCG transportation barrier and increase in EBL barrier structure was directly fabricated on the GaN plays the vital role in the improved performance of structure without an airgap. The entire MC structure LDs. The built-in potential affects the EBL band comprised a bottom dielectric distributed Bragg bending. Electric fields due to polarisation, ionised reflector; a GaN cavity; and a top HCG reflector, impurity charge distribution, and externally applied which was designed to yield high reflectance for bias are investigated. It is observed that the step transverse magnetic (TM)- or transverse electric (TE)- graded EBL structurereduces the built-in potential at polarized light. The MC device revealed an operation the EBL interface, thus, resulting in reduced band threshold of approximately 0.79 MW/cm2 when bending as compared to reference laser structure. pulsed optical pumping was conducted using the HCG structure at room temperature. The laser emission was TM polarized with a degree of polarization of

99.2% and had a small divergence angle of 14° (full

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Deep UV Laser at 249 nm Based on GaN Quantum Electrically pumped green lasing action from Wells InGaN/GaN MQW heterojunction with a p-NiO cap Wuhan National Laboratory for Optoelectronics, Huazhong layer University of Science and Technology, Wuhan 430074, School of Physics and Engineering, Henan Key Laboratory People’s Republic of China of Photoelectric Energy Storage Materials and King Abdullah University of Science and Technology Applications, Henan University of Science and Technology, (KAUST), Advanced Semiconductor Laboratory, Thuwal 263 Kaiyuan Avenue, Luoyang 471003, People's Republic of 23955, Saudi Arabia China Ningbo Institute of Materials Technology and Engineering, Key Laboratory of Materials Physics of Ministry of Chinese Academy of Sciences, Ningbo, 315201 Zhejiang, Education Department of Physics and Engineering, People’s Republic of China Zhengzhou University, Zhengzhou 450052, People's Republic of China ACS Photonics School of Physics and Electronic Engineering, Jiangsu https://doi.org/10.1021/acsphotonics.9b00882 Normal University, Xuzhou 221116, People's Republic of China In this Letter, we report on deep UV laser emitting at Jilin Provincial Key Laboratory of Architectural Electricity & 249 nm based on thin GaN quantum wells (QWs) by Comprehensive Energy Saving, School of Electrical optical pumping at room temperature. The laser Engineering and Computer, Jilin Jianzhu University, threshold was 190 kW/cm2 that is comparable to Changchun, 130118, People's Republic of China state-of-the-art AlGaN QW lasers at similar Materials Research Express wavelengths. The laser structure was https://doi.org/10.1088/2053-1591/ab33aa pseudomorphically grown on a c-plane sapphire substrate by metalorganic chemical vapor deposition, Electrically pumped green lasing action has been comprising 40 pairs of 4 monolayer (ML) GaN QWs achieved from an In0.23Ga0.77N/GaN multi quantum sandwiched by 6 ML AlN quantum barriers (QBs). The well heterojunction with a p-NiO cap layer. The NiO low threshold at the wavelength was attributed to epilayer grown by photo-assisted metal organic large optical and quantum confinement and high chemical vapor deposition (MOCVD) showed high quality of the material, interface, and Fabry-Pérot crystal quality with cubic NaCl morphological facet. The emissions below and above the threshold structure. Under forward bias, distinct diode were both dominated by transverse electric rectification characteristics were obtained and the polarizations thanks to the valence band turn-on voltage was about 2.0 V. Increasing the characteristics of GaN. This work unambiguously current to 30 mA, strong sharp lasing peaks with demonstrates the potentials of the binary AlN/GaN narrower line width of 0.8 nm was detected. The heterojunctions for high-performance UV emitters. lasing mechanism and current transport of the diode were studied through the aspects of energy band structure of the diode.

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GROUP 3 - Power Electronics Group leader: Frédéric Morancho (LAAS-CNRS) Information selected by Frédéric Morancho (LAAS-CNRS) and Yvon Cordier (CRHEA-CNRS)

Epitaxial regrowth and characterizations of vertical junction diodes. Quasi-vertical diodes with a 20 nm GaN transistors on silicon thick, magnesium concentration of 2 × 1020 cm−3 Research Center for Nano-Devices and Advanced layer on top of a 480 nm thick layer with a Materials, Nagoya Institute of Technology, Nagoya, 466- magnesium concentration of 1018 cm−3 show greatly 8555 Japan increased forward current density – >100× higher – Innovation Center for Multi-Business of Nitride than those with a 500 nm thick uniformly Semiconductors, Nagoya Institute of Technology, Nagoya, 3 × 1019 cm−3 Mg-doped p-layer. Forward knee 466-8555 Japan voltage and ideality factor are reduced by a factor of

Semiconductor Science and Technology more than two, and reverse leakage current density https://doi.org/10.1088/1361-6641/ab3154 is also reduced. Additionally, the specific differential series resistance is reduced significantly. With We report the fabrication of fully-vertical GaN-based photoluminescence measurements, we found that metal-oxide-semiconductor field-effect transistors (V- these improvements are largely due to improved p- MOSFETs) on Si. A p-GaN current aperture was GaN material quality of the high/low junction sample introduced in the vertical device epi-structure using with lower average Mg concentration. plasma-based dry etching and epitaxial regrowth technique to control the vertical current conduction. Steep Subthreshold Swing in GaN Negative The fabricated V-MOSFET exhibited drain current Capacitance Field-Effect Transistors density of 2.5 kA cm−2 with ON-resistance (R ON ) of School of Physics and Technology, Wuhan University, 4.3 mΩ-cm2. The transfer characteristics of the Wuhan 430072, China Science and Technology on Monolithic Integrated Circuits device showed a peak trans-conductance (G m,max) and Modules Laboratory, Nanjing Electronic Device of 248 S cm−2 with a threshold voltage (V th ) of Institute, Nanjing 210016, China −18.7 V during OFF-to-ON-state sweeping. However, Key Laboratory for Micro-/Nano-Optoelectronic Devices of a blocking voltage of 36.5 V (drain current density 0.3 Ministry of Education, School of Physics and Electronics, kA cm−2) was observed under an OFF-state condition Hunan University, Changsha 410082, China of the device which needs further improvement for the high-power device applications. IEEE Transactions on Electron Devices https://doi.org/10.1109/TED.2019.2934181 Improved electrical performance of MOCVD-grown GaN p-i-n diodes with high-low junction p-layers Due to the Boltzmann distribution of carriers, the Department of Physics, Applied Physics, and Astronomy, subthreshold swing (SS) of traditional metal-oxide- Rensselaer Polytechnic Institute, 110 8th St, Troy, NY semiconductor field-effect transistors (MOSFETs) is 12180, USA above 60 mV/dec at room temperature. In this Department of Electrical & Computer Systems Engineering, article, GaN-based negative capacitance field-effect Rensselaer Polytechnic Institute, 110 8th St, Troy, NY transistors (NCFETs) were fabricated by introducing 12180, USA HfO₂ /P(VDF-TrFE) stack as the gate dielectric layer. Taiyo Nippon Sanso Corporation, 10 Ohkubo, Tsukuba 300- With the voltage amplification effect of the 2611, Japan ferroelectric, the GaN NCFETs demonstrate the

Solid-State Electronics ultralow SS value of 36.3 mV/dec at room https://doi.org/10.1016/j.sse.2019.107646 temperature, which also advances the MOSFETs in terms of saturation current (633.4 μA/μm) and on-off We report that using a high/low p-type junction ratio (>10⁷ ). Therefore, this article demonstrates the anode structure results in improved hole injection feasibility of NCFETs for breaking the Boltzmann limit over a uniformly-doped p-anode layer in GaN pin in III-V semiconductors-based transistors and opens

GaNEX | III-N Technology Newsletter No. 81 | 14 up an avenue for switching electronic devices for Dynamic Behavior Improvement of Normally-off p- portable applications. GaN High-Electron-Mobility Transistor Through a Low-Temperature Microwave Annealing Process Gate Reliability of p-GaN HEMT With Gate Metal Department of Electronic Engineering, Chang Gung Retraction University, Taoyuan 333, Taiwan Advanced Research Center on Electronic System, Department of Radiation Oncology, Chang Gung Memorial Department of Electrical, Electronic, and Information Hospital, Taoyuan 333, Taiwan Engineering, University of Bologna, 47522 Cesena, Italy College of Engineering, Ming Chi University of Technology, imec vzw, B-3001 Leuven, Belgium Taipei 243, Taiwan Ghent University, B-9052 Ghent, Belgium Episil-Precision Inc., Hsinchu 300, Taiwan, R.O.C. Department of Electronics Engineering, Feng Chia IEEE Transactions on Electron Devices University, Taichung 407, Taiwan https://doi.org/10.1109/TED.2019.2938598 IEEE Journal of the Electron Devices Society In this article, we present an analysis of the gate https://doi.org/10.1109/JEDS.2019.2941519 degradation induced by long-term forward gate stress in GaN-based power HEMTs with p-type gate, The surface morphology optimization of ohmic controlled by a Schottky metal-retracted/p-GaN contacts and the Mg out-diffusion suppression of junction. In particular, time-dependent gate normally off p-GaN gate high-electron-mobility breakdown and threshold voltage instability are transistors (HEMTs) continue to be challenges in the investigated as function of different geometries, gate power electronics industry in terms of the high- biases, and temperatures. The introduction of a gate frequency switching efficiency. In this study, better metal retraction (GMR) process step improves the current density and reliable dynamic behaviors of p- device lifetime because it suppresses the onset of the GaN gate HEMTs were obtained simultaneously by leakage current flow occurring at the gate edges for adopting low-temperature microwave annealing relatively high gate voltage. However, biasing GMR p- (MWA) for the first time. Moreover, HEMTs GaN HEMT at VG > 8 V and T > 80 °C, a new fabricated using MWA have a higher ION/IOFF ratio degradation mechanism shows up, possibly altering and lower gate leakage current than the HEMTs the lifetime even at low VG operation. Main results in fabricated using rapid thermal annealing. Due to the this article demonstrate that although at high VG and local heating effect, a direct path for electron flow high T, a localized degradation effect ascribed to the can be formed between the two-dimensional device isolation region is responsible for time- electron gas and the ohmic metals with low bulges dependent gate breakdown, thanks to GMR higher surface. Moreover, the Mg out-diffusion of p-GaN operating voltages compatible with ten-year gate layer was also suppressed to maintain good continuous operation is attained. Finally, the longer current density and low interface traps. device lifetime at moderate VG values brought by GMR allows evaluating the threshold voltage More than 3000 V Reverse Blocking Schottky-Drain instability for long stress times (≈112 h) at relatively AlGaN-Channel HEMTs with > 230 MW/cm2 Power high VG and high T, leading to the observation of a Figure-of-Merit Key Laboratory of Wide Band Gap Semiconductor saturation of the long-term positive threshold voltage Materials and Devices, School of Microelectronics, Xidian shift and providing additional information about the University, Xi’an 710071, P. R. China underlying physical degradation mechanisms. Overall, the saturated 0.65-V Δ VTH under worst-case IEEE Electron Device Letters condition (VG = 7 V at 150 °C, i.e., corresponding to https://doi.org/10.1109/LED.2019.2941530 ten-year lifetime) reveals a reliable and fairly stable technology with respect to forward gate stress. In this letter, more than 3000 V reverse blocking Schottky-drain AlGaN-channel HEMTs are demonstrated for the first time. By using Schottky drain technology, forward breakdown voltage VFB (at

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10 µA/mm) is improved from 1850 2100 V to 2200 off limits of vertical GaN-based conventional doped 2600 V for LGD = 22 m. Due to the high breakdown pn superjunction (SJ) and natural polarization electric field of AlGaN material, reverse blocking superjunction (PSJ) devices using analytical models voltage VRB (at 10 µA/mm) reaches as high as -1950 - and numerical simulations. We have obtained much 2200 V. For HEMTs with LGD = 52 µm, record high better performance on the vertical natural VFB of > 3000 V and VRB of >-3000 V have been polarization superjunction devices based on the achieved. The leakage current is as low as 6.06 AlGaN/GaN and AlInN/GaN heterostructures instead nA/mm at VDS = -2000 V. of the conventional superjunction devices with alternating doped p/n pillars. Our results show that Demonstration of 1.27 kV etch-then-regrow GaN p-n the drift-region Ron,sp of vertical GaN-based junctions with low leakage for GaN power superjunction devices is one to more than four orders electronics of magnitude lower than the 1D limit of GaN School of Electrical, Computer, and Energy Engineering, conventional unipolar devices at the same BV. For 1 Arizona State University, Tempe, AZ, 85287 USA and 10 kV devices, the optimized specific on- resistance of the drift region is about 10 and 300 IEEE Electron Device Letters times lower for conventional superjunction devices, https://doi.org/10.1109/LED.2019.2941830 but 1000 and 20 000 times lower for natural

This letter reports high performance GaN p-n polarization superjunction devices. junctions with regrown p-GaN by metalorganic Oxygen-based digital etching of AlGaN/GaN chemical vapor deposition (MOCVD) on dry-etched structures with AlN as etch-stop layers surfaces. The breakdown voltage reaches 1.27 kV and School of Microelectronics, Southern University of Science the differential on-resistance is 0.8 mΩ·cm2. The and Technology, Shenzhen 518055, China effects of etching powers and surface treatments on Department of Electric and Electronics Engineering, the reverse leakage characteristics of the regrown p- Southern University of Science and Technology, Shenzhen n junctions have been investigated. It’s found that 518055, China lowering the etching power and damage is very Harbin Institute of Technology, Harbin 150001, China effective to reduce the leakage currents and increase Department of Electronic and Computer Engineering, Hong the breakdown voltages. Further analysis reveals that Kong University of Science and Technology, Hong Kong the charge concentration at the regrowth interface 0000, China plays a critical role in the performance of the regrown Department of Microelectronics, Delft University of Technology, Delft 2600 GB, Netherlands samples. To avoid sacrificing the etching rate by using Department of Materials Engineering, the University of only low power etching, a multiple-RF-power etching British Columbia, Vancouver, British Columbia V6T 1Z4, recipe was developed with gradually decreased Canada etching power. This work has demonstrated a GaN Device Engineering Technology Research Center of practical and viable method to realize high Guangdong, Southern University of Science and performance regrown p-n junctions for various Technology, Shenzhen 518055, China advanced GaN power electronics. The Key Laboratory of the Third Generation Semiconductors, Southern University of Science and Performance limits of vertical GaN of conventional Technology, Shenzhen 518055, China doped pn and natural polarization superjunction Journal of Vacuum Science & Technology A devices https://doi.org/10.1116/1.5115427 Center for Integrated Electronics, Rensselaer Polytechnic

Institute, Troy, New York 12180, USA O2 plasma-based digital etching of Al0.25Ga0.75N

Applied Physics Letters with a 0.8 nm AlN spacer on GaN was investigated https://doi.org/10.1063/1.5109389 using an inductively coupled plasma etcher. Silicon oxide layer was used as the hard mask. At 40 W RF We have determined and evaluated the specific on- bias power and 40 sccm oxygen flow, the etch depth resistance (Ron,sp) vs breakdown voltage (BV) trade- of Al0.25Ga0.75N was 5.7 nm per cycle. The 0.8 nm

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AlN spacer layer acted as an etch-stop layer in three aluminum nitride layer shows a time dependent cycles. The surface roughness improved from 0.66 to breakdown, with Weibull-distributed failures and a 0.33 nm after the three and seven digital etch cycles. shape factor greater than 1, in line with the Compared to the dry etch only approach, this percolation model. technique smoothed the surface instead of causing surface roughening. Compared to the selective ESD-failure of E-mode GaN HEMTs: Role of device thermal oxidation with a wet etch approach, this geometry and charge trapping method is less demanding on the epitaxial growth Department of Information Engineering, University of and saves the oxidation process. It was shown to be Padova, Italy effective in precisely controlling the AlGaN etch ON Semiconductor, Oudenaarde, Belgium depth required for recessed-AlGaN HEMTs. CMST, University of Ghent, Belgium

Microelectronics Reliability Buffer breakdown in GaN-on-Si HEMTs: A https://doi.org/10.1016/j.microrel.2019.06.026 comprehensive study based on a sequential growth experiment We investigate the robustness of E-mode GaN HEMTs Department of Information Engineering, University of under ESD testing; specifically, we focus on three Padova, 35131 Padova, Italy aspects, i.e. the impact of gate bias on TLP failure EpiGaN, 3500 Hasselt, Belgium IEMN-CNRS, 59652 Villeneuve d'Ascq, France voltage, the role of device geometry (with focus on gate length), and the difference in failure voltage Microelectronics Reliability when tests are carried out under UV illumination. The https://doi.org/10.1016/j.microrel.2019.113461 results demonstrate that: (i) when the transistors are tested in semi-on and on-state (4 V < VGS < 6 V), The aim of this work is to investigate the breakdown failure occurs due to a current-dependent process mechanisms of the layers constituting the vertical and failure takes place at a random position along the buffer of GaN-on-Si HEMTs; in addition, for the first gate finger, as demonstrated by optical inspection; time we demonstrate that the breakdown field of the (ii) gate geometry strongly impacts on TLP stability; AlN nucleation layer grown on a silicon substrate is specifically, devices with larger gate length have a equal to 3.2 MV/cm and evaluate its temperature better robustness, possibly due to the lower drain dependence. To this aim, three samples, obtained by current (higher on-resistance) and the lower power stopping the epitaxial growth of a GaN on Silicon dissipation. (iii) We find that under UV light the TLP stack at different steps, are studied and compared: robustness is slightly improved. This is ascribed to a Si/AlN, Si/AlN/AlGaN, full vertical stack up to the “beneficial” effect of traps; however, the effect is Carbon doped buffer layer. The current-voltage (IV) much less than in previous reports, possibly due to a characterizations performed at both room much better epitaxial quality. temperature and high temperature show that: (i) the defectiveness of the AlN nucleation layer is the root Power GaN FET boards thermal and electromagnetic cause of the leakage through an AlN/Silicon junction, optimization by FE modeling and causes the vertical I-V characteristics to have a Department of Engineering and Architecture, University of high device-to-device variability; (ii) the first AlGaN Parma, Parco Area delle Scienze 181/a, 43124 Parma, Italy layer grown over the AlN, beside improving the breakdown voltage of the whole structure, causes the Microelectronics Reliability https://doi.org/10.1016/j.microrel.2019.113466 leakage current to be more stable and uniform across the sample area; (iii) a thick strain-relief stack and a This work deals with optimization of boards with carbon-doped GaN buffer enhance the breakdown commercial discrete power GaN FETs in applications voltage up to more than 750 V at 170 °C, and where natural air convection is a strict constraint. In guarantee a remarkably low device-to-device these cases, both thermal and electromagnetic variability. Furthermore, a set of constant voltage behaviours are critical reliability issues for the board stress on the Si/AlN sample demonstrate that the design, and they are modeled by Finite Element (FE)

GaNEX | III-N Technology Newsletter No. 81 | 17 analysis, starting from literature description of the On the other hand, the Pb5Sn solder joined structure device structure, and measurements on a simple test showed a 50% reduction in shear strength after circuit. For improved accuracy and more realistic 500 cycles compared to the initial state. Some modeling, verification and validation simulation steps disadvantages of these solder joints occurred such as are introduced, in order to evaluate the relevant an intermetallic compound and interface error parameters for different FEM solutions. The degradation. Thus, with the new design and results obtained demonstrate a good fitting with evaluation reported in this study, Ag sinter joining experimental and make it possible to improve board can be expected as an environment-friendly thermal characteristic. The electromagnetic replacement die material for the long-term reliability simulations allow the evaluation, and possibly the of WBG semiconductor module packaging. reduction, of parasitic inductances for different layouts. Then, the proposed approach enables Power cycling and temperature endurance test of a thermal and electromagnetic optimization of the GaN switching cell with substrate integrated chips layout design by simple FEM simulations, without any Technical University of Applied Sciences Rosenheim, preliminary prototype, with time and cost saving. Rosenheim 83024, Germany Chair of Electrical Drive Systems and Power Electronics, Development of high-strength and superior thermal Technical University Munich, Munich 80333, Germany shock-resistant GaN/DBA die attach structure with Microelectronics Reliability Ag sinter joining by thick Ni metallization https://doi.org/10.1016/j.microrel.2019.06.064 Department of Adaptive Machine Systems, Graduate

School of Engineering, Osaka University, Osaka, Japan We present a reliability study of a half-bridge The institute of Scientific and Industrial Research, Osaka University, Ibaraki-Shi 567-0047, Japan switching cell with substrate integrated 650 V GaN Joining and Welding Research Institute, Osaka University, HEMTs. Power Cycling Testing with a ΔTj of 100 K has Ibaraki-Shi 567-0047, Japan revealed thermo-mechanically induced failures of Power Conversion Engineering Team, Hyundai Mobis Co., contact vias after more than 220 kcycles. The via Ltd, Yongin-Shi 449-912, Republic of Korea failure mode of contact opening is confirmed by reverse-bias pulsed IV-measurements to be primarily Microelectronics Reliability triggered by a ΔTj imposed thermal gradient and not https://doi.org/10.1016/j.microrel.2019.06.072 by a high Tj. The chip electrical characteristics,

however, remained unaffected during Power Cycling. With the advent of wide band-gap (WBG) Furthermore, a High Temperature Storage test at semiconductors like silicon carbide (SiC) and gallium 125 °C for 5000 h has shown no changes in the nitride (GaN), the operation temperature of WBG electrical performance of substrate integrated GaN power modules are expected to be over 250 °C. High HEMTs. temperature die-attach materials that can withstand these harsh conditions are emerging as one of the Degradation indicators of power-GaN-HEMT under main issues of the reliability of power electronic switching power-cycling applications. In this study, high-strength and superior Centre National d'Études Spatiales, Toulouse, France thermal shock-resistant GaN/DBA die attach LAAS-CNRS, Toulouse, France structures with Ag sinter joining by thick Ni IRT Saint-Exupéry, Toulouse, France metallization (7 μm) were developed and compared to conventional Pb5Sn soldering die attach. A thermal Microelectronics Reliability shock test was conducted at a temperature range of https://doi.org/10.1016/j.microrel.2019.113412 −50/250 °C, holding 30 min at each extreme temperature up to 500 cycles. Consequently, the This paper describes the design of a power-cycling shear strength of the Ag sinter joining structure was test bench to study the reliability of power-GaN- sustained above the initial strength after 500 cycles, HEMT power switches. The aim of the presented which showed durable sinter necks and non- paper is to study the measurable electrical deformed interfaces due to the thick Ni metallization. consequences of internal degradation with aging. The

GaNEX | III-N Technology Newsletter No. 81 | 18 shift of these measured parameters can be Insights into the off-state breakdown mechanisms in considered as reliability indicators. With the aim to power GaN HEMTs decorrelate thermomechanical effects from internal DIEF, Univ. of Modena and Reggio Emilia, Modena, Italy GaN-specific degradation, the temperature was DISMI and EN&TECH, Univ. of Modena and Reggio Emilia, limited by choosing the stress parameters with the Reggio Emilia, Italy use of an infrared camera. The power-cycling test Microelectronics Reliability was designed with GaN-specific gate drivers to https://doi.org/10.1016/j.microrel.2019.06.066 consider the pGaN-gate requirements. Thorough the power-cycling test we have tracked the evolution of We analyze the off-state, three-terminal, lateral electrical parameters that have been identified as breakdown in AlGaN/GaN HEMTs for power switching degradation indicators. Finally, we have studied the applications by comparing two-dimensional link between the stress parameters and the numerical device simulations with experimental data degradation, as well as the correlation between from device structures with different gate-to-drain different degradation indicators. spacing and with either undoped or Carbon-doped

GaN buffer layer. Our simulations reproduce the Dynamic characterization of SiC and GaN devices different breakdown-voltage dependence on the with BTI stresses gate-drain-spacing exhibited by the two types of School of Engineering, University of Warwick, Coventry, UK device and attribute the breakdown to: i) a Faculty of Engineering, University of Bristol, Bristol, UK combination of gate electron injection and source- Microelectronics Reliability drain punch-through in the undoped HEMTs; and ii) https://doi.org/10.1016/j.microrel.2019.06.081 avalanche generation triggered by gate electron injection in the C-doped HEMTs. The use of temperature sensitive electrical parameters for condition monitoring of power Investigation of the degradations in power GaN-on- devices is widely acknowledged for conventional Si Si MIS-HEMTs subjected to cumulative γ-ray power devices. However, its use for wide bandgap irradiation devices is still the subject of research thereby making International College of Semiconductor Technology, the electrothermal characterization of these devices National Chiao Tung University, Hsinchu, Taiwan a requirement, especially for GaN power devices. This Department of Physics, Indian Institute of Technology Delhi, HauzKhas, New Delhi, India paper investigates and compares the dynamic Department of Information Engineering, University of characteristics of SiC and GaN power devices and Padova, Padova, Italy how these characteristics are affected by bias temperature instability from gate voltage stress. Microelectronics Reliability Results show that turn-ON dID/dt increases with https://doi.org/10.1016/j.microrel.2019.06.041 temperature in SiC whereas it decreases with temperature in GaN. Turn-OFF dVDS/dt is marginally In this work, GaN-on-Si power Metal-Insulator- temperature dependent in both technologies. These Semiconductor High Electron Mobility Transistors electrical parameters can be subject to drift from (MIS-HEMTs) are irradiated through different regimes gate oxide degradation due to charge trapping and of cumulative γ-ray irradiation, namely 1, 2, 3, 4, and threshold voltage drift. Initial VGS stress tests (at the 5 kGy for the first sample; 1, 3, and 5 kGy for the rated voltages) on SiC and GaN devices show no second sample; 1, 5, and 10 kGy for the third sample; apparent shift in VTH, however more sophisticated and 1, 10, and 20 kGy for the fourth sample. After test methods using the body diode voltage as an each irradiation dose, drain current (ID), threshold indicator for VTH showed rapid VTH shift and voltage (VTh), and gate leakage current (Ig) are recovery (within a few seconds) in SiC MOSFETs. electrically characterized in all the samples. An improvement in ID with a shift in VTh is observed in all the samples, which saturates after a higher irradiation dose. X-ray photoelectron spectroscopy

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(XPS) analysis confirms creation of nitrogen vacancies characterized by measurements. Finally, the that act as donor and improves the ID. No significant influence of the measured power semiconductors change in Ig is observed except for an increase in performance on the overall efficiency and power noise in gate leakage current. Scanning electron density of a typical converter is determined through a microscopy (SEM) shows the Al-based metallization case study analyzing a hard switching half-bridge pad degrades due to formation of small cavities. operated as single-phase inverter, i.e. the Finally, energy dispersive X-ray (EDX) analysis fundamental building block of several M/ML confirms the formation of Al native oxides due to γ- topologies. It is concluded that, in this voltage and ray irradiation. power class, GaN e-FETs are nowadays approximately a factor of three superior to Si Power MOSFETs; Experimental Characterization of Silicon and Gallium however, the better heat dissipation achieved by the Nitride 200V Power Semiconductors for latter still makes them the preferred solution for Modular/Multi-Level Converters Using Advanced higher power applications. Measurement Techniques Power Electronic Systems Laboratory, ETH Zurich, Reduction of leakage current in GaN Schottky diodes Switzerland through ultraviolet/ozone plasma treatment Infineon Technologies Austria AG, Austria Department of Electrical and Computer Engineering and Department of Electronic and Electrical Convergence IEEE Journal of Emerging and Selected Topics in Power Engineering, Hongik University, Sejong 30016, Korea Electronics Department of Physics, University of Wisconsin-Madison, https://doi.org/10.1109/JESTPE.2019.2944268 Madison, WI 53706, USA

The increasing demand for higher power densities IEEE Electron Device Letters and higher efficiencies in power electronics, driven by https://doi.org/10.1109/LED.2019.2944353 the aerospace, electric vehicle and renewable energy industries, encourages the development of new Surface passivation is critically important to improve converter concepts. In particular, modular and/or the leakage current and current on/off ratio in multi-level (M/ML) topologies are employed to break Schottky diodes and thus the overall device the performance barriers of state-of-the-art power performance and reliability. In this work, we report converters by simultaneously reducing the system the reduction of leakage current in Pt/n-GaN and losses and volume/weight. These improvements Pd/n-GaN Schottky diodes by improving metal-GaN mainly originate from the replacement of high interface passivation using ultraviolet/ozone (UV/O3) voltage transistors, typical of two-level converters, plasma treatment. X-ray photoelectron spectroscopy with low voltage, e.g. 200V, devices, offering superior was used to verify the improved passivation at the electric performance. Hence, two low on-state surface of GaN. Capacitance-voltage measurements resistance silicon (Si) and gallium nitride (GaN) 200V were employed to determine the change in built-in power semiconductors are comprehensively potentials and the Schottky barrier heights of the characterized in this paper to support the multi- Schottky diodes. Temperature-dependent objective optimization and the design of M/ML measurements of current-voltage characteristics power converters. First, the selected devices are verified the thermionic emission carrier injection analyzed experimentally determining their mechanisms. It was found that the leakage current in conduction, thermal and switching characteristics; for the GaN Schottky diodes was reduced by three orders this purpose, a novel ultra-fast transient calorimetric of magnitude and the current on/off ratio was measurement method is introduced and explained in increased by two orders of magnitude due to the detail. In the course of this analysis, an unexpected interface passivation that reduced defect states at switching loss mechanism is observed in the Si metal-semiconductor interfaces and suppressed devices at hand; the physical reason of this behavior dislocation-induced leakage current. is clarified and it is proven to be solved in next generation research samples, which are also

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Stress dependent degradation mechanisms on study focuses on the failure observed during the commercially available GaN Normally-Off transistors short circuit of these devices when the test voltage is More Electrical Aircraft department, IRT Saint Exupery, larger than 350 V. In this failure mode, the energy 31432 Toulouse, France involved is quite low and the time to failure is <1 μs. Thales Alenia Space France, 31037 Toulouse, France Simulation results show that in these test conditions HIREX Engineering, 31520 Ramonville Saint Agne, France a very high-power density is dissipated in a critical

region of the device and it is intensified by a Microelectronics Reliability significant current focalization which has been https://doi.org/10.1016/j.microrel.2019.06.020 proved by experimental observations. It is In this paper, a series of stress test experiments were demonstrated that the temperature in the critical carried out on GaN Normally-Off COTS transistors region can reach the maximum allowable (eGaN-on-Si) accelerating the normal degradation temperature for a GaN/AlGaN structure. process through the use of elevated temperature and biasing conditions. The primary objective is to build a Evidence of Mg segregation to threading dislocation predictive model of the reliability of such GaN in normally-off GaN-HEMT Normandie Univ, UNIROUEN, INSA Rouen, UMR CNRS electronic components used in power conversion. 6634, 76000 Rouen, France, Groupe de physique des The experiments were performed on 80 samples materiaux, 129641 Sainte Etienne du Rouvray, Haute- allocated in: i) four conditions of DC off-state and on- Normandie France pulsed step stress sequences, ii) three high temperature off-state endurance lifetest sequences, IEEE Transactions on Nanotechnology iii) and three on-pulsed lifetest sequences. These https://doi.org/10.1109/TNANO.2019.2942400 series of high temperature step stress and lifetest conditions allow to identify and separate the infant In this article, the segregation of Mg to threading mortality from the random to wear-out mechanisms dislocation is demonstrated in a commercial occurring in accelerated DC off state, forward-gate normally-off GaN High Electron Mobility Transistor and pulsed high current drain testing. Eyring model using atom probe tomography. The diffusion of Mg was determined based on Weibull plot data analysis from a doped p-type GaN gate through the AlGaN allowing to quantify a wearout failure mechanism buffer to the GaN substrate is demonstrated. consisting in the shortening of the gate junction. The n factor of the inverse power law of the off-state Impact of defects on the electrical properties of p–n voltage at 150 °C channel was determined to be 7. diodes formed by implanting Mg and H ions into N- On-pulsed experiments carried out at Idspulse = 16A polar GaN for 3 junction temperatures demonstrated Rdson Toyota Central R&D Labs., Inc., Yokomichi, Nagakute 480- degradation and an activation energy of 1.28 eV 1192, Japan Division of Applied Physics, Faculty of Pure and Applied (failure criteria 50% drift on Idsonmax). Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573,

Japan Failure mechanisms of enhancement mode GaN power HEMTs operated in short circuit Journal of Applied Physics Department of Electrical and Information Engineering https://doi.org/10.1063/1.5116886 “Maurizio Scarano”, University of Cassino and Southern Lazio, Cassino, Italy The relationship between the junction properties and

point defects in p–n diodes, formed by implanting Microelectronics Reliability magnesium (Mg) and hydrogen (H) ions into a GaN https://doi.org/10.1016/j.microrel.2019.113454 layer, was investigated. Vertical diodes were The paper reports the results of a study based on fabricated by implanting Mg ions with and without H experimental data and finite element simulations ions into nitrogen-polar n-type GaN substrates, about the failure mechanism of 650 V p-doped GaN followed by annealing at 1150 °C or 1230 °C without power HEMT operated in short circuit condition. The the use of protective layers. Samples annealed at

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1150 °C showed Schottky-barrier-diode (SBD)-like Measurement of avalanche multiplication utilizing properties with an insufficient build-in potential, Franz-Keldysh effect in GaN p-n junction diodes with indicating surface depletion due to poor activation of double-side-depleted shallow bevel termination Mg acceptors. The Mg/H-ion-implanted diode Department of Electronic Science and Engineering, Kyoto annealed at 1230 °C exhibited an improved rectifying University, Kyoto 615-8510, Japan property with a build-in potential around 3 V, close to Toyota Central R&D Labs., Inc., Nagakute, Aichi 480-1118, an ideal p–n junction of GaN, whereas the sample Japan Institute of Materials and Systems for Sustainability with only implanted Mg-ions exhibited mixed (IMaSS), Nagoya University, Nagoya 464-8603, Japan properties of a p–n junction and SBD due to Department of Electronics, Nagoya University, Nagoya imperfect activation. In addition, leakage currents in 464-8603, Japan the forward bias below 3 V for the Mg/H-ion- implanted diodes can be explained by a Applied Physics Letters recombination current based on the Shockley–Read– https://doi.org/10.1063/1.5114844 Hall model with an estimated recombination lifetime of 3 to 10 ps. To clarify the sources of the difference Avalanche multiplication characteristics of GaN p-n in the junction properties, positron annihilation junction diodes (PNDs) with double-side-depleted spectroscopy was employed. The samples annealed shallow bevel termination, which exhibit nearly ideal at 1150 °C contained high-density vacancy clusters avalanche breakdown, were investigated by such as (VGaVN)3, whose concentrations were photomultiplication measurements using sub- reduced by the higher temperature annealing. We bandgap light. In GaN PNDs under reverse bias found that introduced H atoms can enhance the conditions, optical absorption induced by the Franz- activation of Mg acceptors and/or reduce the defect Keldysh (FK) effect is observed, resulting in a concentrations. The results indicate the combination predictable photocurrent. The avalanche of the H ion introduction and higher temperature multiplication factors were extracted as a ratio of the annealing improves the junction properties. measured values to the calculated FK-induced photocurrent. In addition, the temperature dependences of the avalanche multiplications were

also investigated.

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GROUP 4 - Advanced Electronics and RF Group leader: Jean-Claude Dejaeger (IEMN) Information selected by Jean-Claude Dejaeger (IEMN) and Yvon Cordier (CRHEA-CNRS)

Investigation of angstrom-thick aluminium oxide stubs matching network (MN). It is noted that the passivation layers to improve the gate lag modified structure, with good design convenience performance of GaN HEMTs and great frequency selectivity, especially in the roll- Department of Electrical and Electronics Engineering, off region between the highest frequency of the Bilkent University, 06800 Ankara, Turkey desired band ( f H ) and second harmonic of the Nanotechnology Research Center, Bilkent University, lowest frequency of the band (2 f L ), is for the first 06800 Ankara, Turkey time employed to design PAs with more optimal UNAM-Institute of Materials Science and Nanotechnology, Bilkent University, 06800 Ankara, Turkey performance and greater bandwidths (BWs). A step- Department of Energy Engineering, Faculty of Engineering, by-step design procedure of the proposed structure is Ankara University, 06830 Ankara, Turkey presented. Experimental results show that using a 10- Department of Physics, Bilkent University, 06800 Ankara, W Wolfspeed GaN HEMT device, a highly efficient Turkey broadband Class-J PA is realised from 1.4 to 2.4 GHz (fractional BW = 52.6%) with measured drain Materials Research Express efficiency of 63.0–68.9% and output power of 39.8– https://doi.org/10.1088/2053-1591/ab2f68 40.3 dBm.

In this paper, we report an angstrom-thick atomic D-Band and G-Band High-Performance GaN Power layer deposited (ALD) aluminum oxide (Al2O3) Amplifier MMICs dielectric passivation layer for an AlGaN/GaN high Fraunhofer Institute for Applied Solid State Physics IAF, electron mobility transistor (HEMT). Our results show 79108 Freiburg, Germany a 55% improvement in the gate lag performance of the design and a decrease by half in interface state IEEE Transactions on Microwave Theory and Techniques density upon coating with two cycles of ALD Al2O3. https://doi.org/10.1109/TMTT.2019.2936558 DC characteristics such as current density, threshold voltage, and leakage currents were maintained. ALD In this article, we present a set of gallium nitride Al2O3 passivation layers with thicknesses up to 10 (GaN) power amplifiers (PAs) that provide state-of- nm were investigated. XPS analyses reveal that the the-art performance within the D-band (110-170 first ALD cycles are sufficient to passivate GaN GHz) and G-band (140-220 GHz) frequencies. A four- surface traps. This study demonstrates that efficient stage cascode PA operates with more than 25 dB of passivation can be achieved in atomic-scale with small-signal gain over a 107-148-GHz band. At 120 dimensions much thinner than commonly used bulk GHz, it can deliver up to 26.4 dBm of output power layers. and up to 16.5% of power-added efficiency (PAE) with more than 26 dB of gain at saturation. The Highly efficient broadband class-J power amplifier combination of these parameters is among the best using modified multisection quarter-wave lines and reported with a solid-state technology at such high short-circuited stubs frequencies. The two G-band circuits are able to School of Microelectronics, Tianjin University, People's provide up to 40 GHz of 3-dB bandwidth and gain Republic of China exceeding 10 dB up to 190 GHz. The measured peak output power is 15.8 dBm at 181 GHz in 0.6-dB gain IET Microwaves, Antennas & Propagation compression with a corresponding PAE of 2.4%. To https://doi.org/10.1049/iet-map.2018.5637 the best of our knowledge, these amplifiers show the

highest gain above 170 GHz and the highest output This study presents a broadband and high-efficiency power above 150 GHz among any reported GaN- Class-J power amplifier (PA)-based on a modified based MMICs. multisection quarter-wave lines and short-circuited

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Analysis of the back-barrier effect in AlGaN/GaN the silicon wafer and matching networks. The high electron mobility transistor on free-standing proposed IMPA enhanced the output power and GaN substrates efficiency compared with the conventional quasi- State Key Laboratory of Luminescence and Applications, monolithic microwave integrated circuit (MMIC) high Changchun Institute of Optics, Fine Mechanics and Physics, power amplifiers (HPAs) due to removal of bonding Chinese Academy of Sciences, Changchun, 130033, wires between matching networks and TR. Further, it People's Republic of China provided a high level of integration and reduces the Department of Electronics Engineering, Chang Gung manufacturing cost associated with the silicon University, Taoyuan, 333, Taiwan interposer technique. For experimental validation, Departments of Radiation Oncology, Chang Gung Memorial Hospital, Taoyuan, 333, Taiwan the proposed WLP IMPA was designed and fabricated The College of Engineering, Ming Chi University of at 10.2 GHz for military radar application. The results Technology, Taishan, 243, Taiwan show that the output power and drain efficiency at Photonic and Institute of Electro-Optical Engineering, saturation point were 48.54 dBm (71.45 W) and National Chiao Tung University, Hsinchu, 300, Taiwan 50.29%, respectively, based on the pulse signal test (100-μs pulsewidth and 10% duty). The dimensions of Journal of Alloys and Compounds the fabricated WLP IMPA were 7.5 mm x 5.8 mm x https://doi.org/10.1016/j.jallcom.2019.152293 0.12 mm.

The effect of AlGaN back-barrier on AlGaN/GaN high Lateral GaN Schottky Barrier Diode for Wireless electron mobility transistors (HEMTs) using free- High-power Transfer Application with High RF/DC standing GaN wafer has been investigated in this Conversion Efficiency: From Circuit Construction and work. With the introducing back-barrier structure, Device Technologies to System Demonstration the leakage path underneath the buffer (native Xidian University, 47905 Xian, Shaanxi China nitrogen-vacancies and GaOx compounds of the MTRC, China HVPE-grown free-standing GaN surface) layer can be suppressed by lift-up the conduction band. As IEEE Transactions on Industrial Electronics compared with AlGaN/GaN HEMTs on SiC wafer, https://doi.org/10.1109/TIE.2019.2939968 AlGaN/GaN HEMTs on free-standing GaN wafer show enhanced drain current (700 mA/mm), improved In this paper, we have carried out a comprehensive transconductance (143 mS/mm), less current collapse study on the wireless power transfer (WPT) concept (12%), higher current gain cut-off frequency (13 GHz), from the rectifier circuit construction and state-of-art and maximum stable gain cut-off frequency (24 GHz), GaN Schottky Barrier Diode (SBD) device technology which is attributed to the higher epi quality layer on to the WPT system demonstration. Benefited from free-standing GaN wafer. the wide bandgap, high mobility and saturation velocity of the GaN 2-dimensional-electron-gas Wafer-Level-Packaged X-Band Internally Matched (2DEG), engineered lateral GaN SBD with low turn-on Power Amplifier Using Silicon Interposer Technology voltage ( Von ) of 0.47 V, on-resistance ( Ron ) of 4 Ω, Division of Electronics and Information Engineering, IT breakdown voltage (BV) of 170 V and junction Convergence Research Center, Chonbuk National capacitance ( Cj ) of 0.32 pF at 0 V bias are achieved, University, Jeonju-si 54896, South Korea which satisfy the fundamental requirements for Wavice Inc., Hwaseong-si 18449, South Korea microwave power rectification. After incorporating the high performance GaN SBD into the optimized IEEE Microwave and Wireless Components Letters rectifier circuit, high RF/DC conversion efficiency of https://doi.org/10.1109/LMWC.2019.2938309 79% is achieved and the input power of per single

In this letter, we propose a wafer-level-packaged GaN SBD is increased by 10X when compared with (WLP) X-band internally matched power amplifier that of a commercial available Si SBD at the same (IMPA) using silicon interposer technology. The efficiency of 50% and frequency of 2.45 GHz. Based proposed WLP IMPA consists of a fully embedded on the rectifier circuit, a microwave power transfer commercial GaN HEMT transistor (TR) embedded in system is constructed with 400 LEDs lighted up,

GaNEX | III-N Technology Newsletter No. 81 | 24 verifying the great promise of adopting high-power samples were made of superconductor-insulator- GaN SBD for the wireless high-power transfer as an superconductor (SIS) trilayers based on Nb/AlN/NbN, alternative energy harvesting technique for future with a gap voltage of about 3.6 mV. The output WPT application. emission was studied using two independent techniques: a THz spectrometer based on the SIS Investigation of trap induced power drift on 0.15 μm receiver with a high spectral resolution (better than GaN technology after aging tests 0.1 MHz) and a Si bolometer. An operating range of United Monolithic Semiconductors, 10 avenue du Québec, the oscillator of 400-580 GHz and a ratio of detected 91140 Villebon-sur-Yvette, France signal to background signal at the receiver output of Laboratoire IMS – Université de Bordeaux, 351 cours de la up to 55 dB are obtained. In addition, a design for the Libération, 33405 Talence, France oscillator with an integrated harmonic mixer for FFO

locking is developed and fabricated using Microelectronics Reliability https://doi.org/10.1016/j.microrel.2019.06.050 Nb/AlOx/Nb trilayers, which is better for FFO operation than Nb/AlN/NbN trilayers at some This paper deals with a power drift occurring during frequencies due to lower surface losses and hence the first hours of aging tests on a 0.15 μm GaN-based better spectral properties. The pumping of the mixer technology. Its purpose is to characterize the kinetic by the FFO output power was measured and found to and the electrical features of this parasitic effect. be sufficient for phase locking. Output power drift has been monitored by substituting interim RF power measurements by Linearity and robustness evaluation of 150-nm pulsed-IV measurements during high temperature AlN/GaN HEMTs reverse bias tests. Moreover, the kinetic of the Department of Information Engineering, University of Padova, via Gradenigo 6/B, 35131 Padova, Italy output power drift has been assessed by reducing the IEMN - CNRS, Institute of Electronics, Microelectronics and time between interim measurements. Additional Nanotechnology, UMR8520 Av. Poincaré, 59650 Villeneuve aging tests were performed at different temperatures d'Ascq, France to found out if the degradation is temperature activated. An interpretation is proposed about an Microelectronics Reliability increase of trap density responsible for drain lag https://doi.org/10.1016/j.microrel.2019.06.080 effect after aging test at temperature higher than room temperature. We report on linearity and robustness of AlN/GaN HEMTs with ultra-thin 4 nm AlN barrier for millimeter Terahertz Source Radiating to Open Space Based on wave range applications. Static and dynamic I-V the Superconducting Flux-Flow Oscillator: characteristics feature high peak transconductance Development and Characterization (gmpeak) of 385 mS/mm, and the transconductance Kotel’nikov Institute of Radio Engineering and Electronics exhibits small changes with gate bias. Semi on-state RAS, Moscow 125009, Russia step stress and 24 h stress tests have been carried Kapteyn Astronomical Institute, University of Groningen, out on representative AlN/GaN HEMTs on SiC 9712 CP Groningen, The Netherlands substrate. No catastrophic failure was identified after semi on-state step stress at VGS = −1.5 V up to IEEE Transactions on Terahertz Science and Technology VDS = 100 V, whereas a gmpeak drop of 26% was https://doi.org/10.1109/TTHZ.2019.2941401 observed in these conditions. Moreover, 24 h stress

We have elaborated, fabricated and tested a carried out at different bias voltage along a load line terahertz source based on the Josephson flux-flow show good robustness of these devices up to oscillator (FFO) integrated with a transmitting lens VDS = 25 V. In addition, an abrupt gate leakage antenna. The oscillator was coupled to the on-chip current increase was identified to be field dependent, double-slot antenna via microstrip lines, and the chip and associated with hot spots identified by was mounted on the silicon lens providing the electroluminescence measurements. Even in continuous terahertz emission output. The oscillator presence of a simple SiN passivation without air

GaNEX | III-N Technology Newsletter No. 81 | 25 bridges or field plates, these devices exhibit high transient measurement technique evaluates power added efficiency up to 40 GHz, thus threshold voltage fluctuations in the 10 μs–100 s demonstrating the great potential of AlN/GaN temporal range, during stress or recovery phases, for heterostructures. different trap-filling configurations. Corresponding recovery transients between 27 °C to 130 °C are Non-destructive techniques for evaluating the analysed to extract a trap activation energy of 0.53– reliability of high frequency active devices 0.56 eV for this technology. Finally, drain and gate LAAS-CNRS and University of Toulouse, Toulouse, France step-stress tests are performed, providing an overview into the robustness of the gate contact Microelectronics Reliability under high electric fields. https://doi.org/10.1016/j.microrel.2019.06.051

S-band pulsed-RF operating life test on AlGaN/GaN SiGe and GaN technologies have achieved rapid HEMT devices for radar application development over the last two decades. High level of University of Rouen Normandy, GPM Laboratory - UMR- RF circuit integration on Si low cost substrates open CNRS 6634, Saint Étienne de Rouvray 76800, France the way for large development of SiGe HBTs, while CEVAA, Technopole du Madrillet, Saint Étienne de Rouvray needs for high power density make GaN HEMT a key 76800, France technology for solid state power modules. As both of DGA-MI, Rennes CEDEX 9 BP7 35998, France these technologies achieve very elevated Thales LAS France, ZI du Mont Jarret, Ymare 76520, France frequencies, they become strong contenders to GaAs technologies. Then reliability studies are needed to Microelectronics Reliability improve the process at the lower technology https://doi.org/10.1016/j.microrel.2019.113434 readiness level scale, and to stabilize the Reliability studies are fundamental to optimize the technological process till the final qualification step. use of new emerging technologies such as To make an efficient diagnostic on the causal origin of AlGaN/GaN HEMTs. This paper reports a reliability the physical root mechanisms involved during the study on two power amplifiers using AlGaN/GaN application of a stress, a multi-tool approach is HEMT in real operating conditions for radar mandatory to secure the diagnostic. In this paper, applications. Three pulsed-RF long aging tests case studies on SiGe HBT and GaN HEMT stressed (8000 h/11,000 h total) are performed under devices are proposed through the cross-analysis of different conditions of (Vds), Temperature, gain low frequency noise spectral densities, of electrical compression and Duty cycle. A following of various transient measurements, and of TCAD simulations. degradation indicators during the aging tests is

Investigation into trapping modes and threshold presented (Pout, Ids, Igs, Rds(on), Gm and Vth). This instabilities of state-of-art commercial GaN HEMTs study will contribute to establish a new reliability Department of Information Engineering, University of prediction model of GaN devices and update the Padova, Padova, Italy FIDES guide.

Microelectronics Reliability Reliability comparison of AlGaN/GaN HEMTs with https://doi.org/10.1016/j.microrel.2019.113464 different carbon doping concentration Dipartimento di Ingegneria dell'Informazione, Università di This work is aimed at investigating the performance Padova, Via Gradenigo 6/A, 35131 Padova, Italy and reliability limits of a commercially available state- of-the-art RF GaN HEMT technology. Measurement Microelectronics Reliability strategies to recognize and assess trap-induced https://doi.org/10.1016/j.microrel.2019.113489 degradations, prevalent in mature technologies, are The reliability of AlGaN/GaN HEMTs adopting Fe and discussed. Double pulsed measurements are used to C co-doping, with high and low carbon doping capture and quantify threshold instabilities, and their concentration was investigated by means of different evolution with temperature, for short quiescent near- stress tests. Firstly, DC and pulsed I-V threshold and off-state stress conditions. A versatile

GaNEX | III-N Technology Newsletter No. 81 | 26 characterization at room temperature are discussed, characteristics in short-channel devices is attributed then drain step stress tests at different gate voltages to the quite small fringing capacitance of the gate. are compared, afterwards, the constant stress at different bias points are discussed. Results show that An Accurate Three-Input Nonlinear Model for Joint the high C HEMTs showed reduced DIBL, smaller Compensation of Frequency-Dependent I/Q leakage current, as well as decreased electric field, Imbalance and Power Amplifier Distortion leading to an improved robustness during on-state School of Electronic Science and Engineering, University of stress testing, with respect to the reference ones. Electronic Science and Technology of China, Chengdu Failure modes during constant voltage stress consist 611731, China in a decrease of drain current and transconductance, Xi'an branch of China Academy of Space Technology, Xi’an 710100, China accelerated by temperature and electric field. School of Microelectronics and Communication

Engineering, Chongqing University, Chongqing 400044, Simulation Investigation of Laterally Downscaled N- China Polar GaN HEMTs State Key Discipline Laboratory of Wide Band Gap IEEE Access Semiconductor Technology, School of Microelectronics, https://doi.org/10.1109/ACCESS.2019.2944025 Xidian University, Xi'an 710071, China Shaanxi Joint Key Laboratory of Graphene, Xi'an 710071, The analog front of the direct conversion transmitter China suffers from the effects of various unavoidable nonlinearities, such as local oscillator (LO) leakage, IEEE Transactions on Electron Devices power amplifier (PA) nonlinearities, and inphase and https://doi.org/10.1109/TED.2019.2940504 quadrature (I/Q) branch amplitude and phase

imbalance, etc. To overcome these nonlinear effects, The N-polar GaN high-electron mobility transistors an accurate three-input nonlinear model is proposed (HEMTs) have demonstrated a powerful performance for joint compensation of frequency-dependent I/Q as the Ga-polar GaN HEMTs. This investigation aims imbalance and PA nonlinear distortion in this paper. to show the direct current performance and cutoff The proposed nonlinear model is an augmented frequency (fT) of the planar N-polar GaN HEMTs with version of the modulator I/Q imbalance gate lengths downscaling from 4 μm to 50 nm by 2-D compensation model, where the magnitudes of the device simulation. The impacts of traps and gate input signal are included as the model input, and a dielectrics and the roles of the field-dependent three-input nonlinear compensation model with mobility and the source and drain series resistances linear parameters is developed. The advantage of the are investigated. For our central-gated device with a proposed model is that the augmented envelope- 10-nm top GaN channel layer, a 30-nm Al0.3Ga0.7N dependent terms can produce the basis function sets barrier layer, and a 3-nm Al₂O₃ gate dielectric, the for compensating the PA nonlinear distortions in the gate length (LG) as the transition point from the long- transmitter. Furthermore, the computational channel behavior to the short-channel one is found to complexity of the proposed model is analyzed in detail for practical digital implementation. To verify be 200 nm. For LG < 200 nm, a linear fT⁻¹ versus LG the validity of the proposed model, the imperfect relation shows up, and notable short-channel effects transmitters based on single-device gallium nitride appear, i.e., the negative shift of the threshold (GaN) PA and GaN Doherty PA, which are driven by voltage, the increase of the drain-induced barrier different communication signals, are used for lowering, and the almost LG-independent constant experimental verification and analysis. The maximum transconductance in the saturation region. experimental results show that the proposed model The degradation of the fTx LG product with the is able to give improved modeling and distortion decrease in the aspect ratio between LG and the mitigation capability than the other reported I/Q equivalent gate-channel distance (tt) is shown to be imbalance compensation methods when the effects quite small. The LG/tt ratio for 15% degradation of of I/Q imbalance and nonlinear characteristics of PA the fTx LG product from its upper limit (19.23 GHz·μ are considered together. m) is 5.5. This small degradation of the frequency

GaNEX | III-N Technology Newsletter No. 81 | 27

Self-Aligned Metal-Semiconductor-Metal Varactors long-term memory effects in single-ended amplifiers, Based on the AlGaN/GaN Heterostructure in this article, we present a feed-forward model to School of Electrical Engineering and Computer Science, calculate this compensation signal in real-time pulsed Gwangju Institute of Science and Technology, Gwangju, radar applications. 61005, Republic of Korea Growth of Millimeter wave AlN/GaN IEEE Electron Device Letters Heterostructures by MOCVD https://doi.org/10.1109/LED.2019.2944720 Science and Technology on Monolithic Integrated Circuits

and Modules Laboratory, Nanjing Electronic Devices The self-aligned metal-semiconductor-metal (SA- Institute, Nanjing, 210016, CHN MSM) structure was utilized to fabricate varactors on top of the AlGaN/GaN heterostructures. The SA-MSM Journal of Crystal Growth structure minimizes the access resistance associated https://doi.org/10.1016/j.jcrysgro.2019.125265 with 2-dimensional electron gas (2DEG), resulting in the significantly improved cutoff frequency. The influences of growth temperature on crystalline Conventional MSM varactors have essentially the quality and electrical properties of thin barrier same cutoff frequency, regardless of the device AlN/GaN heterostructures were studied by metal width. On the other hand, the SA-MSM varactors organic chemical vapor deposition (MOCVD). It is require the optimum device width to obtain the found that the high growth temperature (≥1100℃) is maximum cutoff frequency which has been achieved beneficial to improve the crystalline quality of the with the device width of 20 lm in this study. The AlN barrier layer, but increases the defect density in fabricated SA-MSM varactors exhibit the the GaN buffer layer. The AlN/GaN hetero-interface extrapolated cutoff frequency of 1.96 THz and a quality was deteriorated when high-temperature AlN capacitance switching ratio of 2.51. barrier layer was grown upon low-temperature GaN buffer layer, resulting in a reduction of electron Compensation of Power Amplifier Long-Term mobility. In addition, the growth temperature of the Memory Behavior for Pulsed Radar Applications GaN cap layer affects the stress evolution of wafer Department of Electronics, Telecommunications, and during the cooling process, which influences the Informatics (DETI), Instituto de Telecomunicações, wafer bowing and electrical properties. By optimizing Universidade de Aveiro, Campus Universitário de Santiago, the growth temperature of each functional layer, the 3810-193 Aveiro, Portugal GaN/AlN/GaN heterostructure with a low defect

density and a smooth surface is obtained. The IEEE Transactions on Microwave Theory and Techniques https://doi.org/10.1109/TMTT.2019.2940185 electron mobility at room temperature is 1549 cm2/(V·s) with a sheet resistance value of 504.8 Ω/□, Pulsed radar amplifiers are known to present severe and the root mean square (RMS) of surface long-term memory effects in their pulse-to-pulse roughness is 0.322 nm. Based on the as-grown stability. These are usually attributed to GaN/AlN/GaN heterostructure, a GaN power MMIC electrothermal dynamics or to trapping effects was fabricated, offering an output power of 15dBm originated in gallium-nitride (GaN) HEMTs. Expanding (31.6mW) and power added efficiency (PAE) of 9.3% on our previous work where we devised a method for at 146 GHz. determining a suitable dynamic variation in the HEMT's gate-source voltage for compensating these

GaNEX | III-N Technology Newsletter No. 81 | 28

GROUP 5 – MEMS and Sensors Group leader: Marc Faucher (IEMN) Information selected by Knowmade

Narrowband Impedance Transformer with 100]AlN/[11–20]Al2O3 orientations, respectively. Extremely High Transformation Ratio of 200 Insertion loss (IL), electromechanical coupling

Micro and Nano Technology Laboratory, Department of coefficient (K2), phase velocity ν0 and temperature Electrical and Computer Engineering, University of Illinois coefficient of frequency (TCF) of SAW Rayleigh mode at Urbana– Champaign, Urbana, IL 61801 USA for different AlN film thickness-to-wavelength Lambwave LLC, Irvine, CA 92620 USA ($h/\lambda $) ratios are systematically studied. The School of Information Science and Technology (SIST), measured K2 values in both orientations are higher ShanghaiTech University, Shanghai 201210 China than the calculation results. It is probably due to the

IEEE Electron Device Letters lattice mismatch effect between AlN and Sapphire. https://doi.org/10.1109/LED.2019.2940257 The lattice mismatch effect enlarges K2 values by enlarging the elastic constants. The relationships This paper presents a hybrid narrowband radio between h/λ, ν0, and TCF are discussed. The results frequency (RF) impedance transformer using an indicate that the TCF value is mostly dependent on aluminum nitride (AlN) microelectromechanical the thermal expansion coefficient (TEC, α) in each system (MEMS) resonator and lumped elements. The orientation and the TCF difference in orientations is hybrid transformer consists of an AlN Lamb wave dramatically affected by the ν0 difference. resonator, a parallel inductor, and a set of three lumped-element networks on a printed circuit board Piezo-phototronic effect on quantum well terahertz (PCB). The AlN resonator and the parallel inductor photodetector for continuously modulating form the narrowband response while the lumped wavelength element networks fulfill the high impedance School of Physics, School of Optoelectronic Science and transformation. The transformer has been Engineering, University of Electronic Science and theoretically predicted and experimentally shown to Technology of China, Chengdu, 610054, China achieve a narrow fractional bandwidth (FBW) of 2.2% Multidisciplinary Nanotechnology Centre, College of and an extremely high impedance transformation Engineering, Swansea University, Swansea, SA1 8EN, UK ratio (ITR) of 200. CAS Center for Excellence in Nanoscience, Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Investigation of surface acoustic waves anisotropy Sciences, National Center for Nanoscience and Technology on high-quality AlN/Sapphire grown by hydride (NCNST), Beijing, 100083, China vapor phase epitaxy School of Nanoscience and Technology, University of Department of Modern Physics, University of Science and Chinese Academy of Sciences, Beijing, 100049, PR China Technology of China, People's Republic of China Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Nano Energy Academy of Sciences, People's Republic of China https://doi.org/10.1016/j.nanoen.2019.104091 School of Nano-Tech and Nano-Bionics, University of Science and Technology of China, People's Republic of Piezo-phototronic effect is unique for effectively China controlling semiconductor and photonic properties by strain-induced piezoelectric field. In this work, we Materials Research Express theoretically explore piezo-phototronic effect on https://doi.org/10.1088/2053-1591/ab2c8c intersubband optical absorption of wurtzite-

In this work, anisotropic properties of surface structured AlGaN/GaN quantum well by self- acoustic waves (SAWs) are researched on high consistently solving eight-band kp Hamiltonian and crystalline quality AlN/Sapphire grown by Hydride Poisson equations. Intersubband transition is Vapor Phase Epitaxy (HVPE). The SAW delay lines are associated with the transition of two electronic states so it has longer wavelength due to lower transition fabricated in [11–20]AlN/[1–100]Al2O3 and [1–

GaNEX | III-N Technology Newsletter No. 81 | 29 energy. Strain can also effectively increase absorption wavelength photodetector was realized. The wavelength in Al0.15Ga0.85N/GaN/Al0.05Ga0.95N responsivity of the UV detector reached 172.12 A/W, quantum well by quantum Stark effect. For while that of the visible detector reached 17.5 A/W. Al0.1Ga0.9N/GaN/Al0.05Ga0.95N quantum well, Meanwhile, both photodetectors achieved high absorption wavelength decreases with increasing photocurrent gain, high external quantum efficiency, strain. Quantum efficiency can be sensitively high normalized detection rate, and low noise controlled by strain. This study not only provides the equivalent power. Our study extends the future theory models of piezo-phototronics of intersubband application of dual-wavelength detectors for image transition, but also offers the method for sensing and optical communication. continuously controlling terahertz application by piezo-phototronic effect. Fabrication and Characterization of Dual Coordinate Self Examined Thermal Flow Sensor Arrays based on Monolithic integration of MoS2-based visible Longitudinal Heat Conduction detectors and GaN-based UV detectors School of Changchun University of Science and Technology, State Key Laboratory of Luminescence and Applications, Changchun 130022, Jilin Province, China Changchun Institute of Optics, Fine Mechanics and Physics, School of Harbin University of Science and Technology, Chinese Academy of Sciences, Changchun 130033, China Harbin, 150080, Heilongjiang Province, China Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, IEEE Sensors Journal Beijing 100049, China https://doi.org/10.1109/JSEN.2019.2941531 Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583, Thermal flow sensors have been widely used in wind Singapore energy utilization, dangerous chemicals detection, Shenzhen Castle Security Technology Co., Ltd., Shenzhen automobiles, intelligent robots and unmanned aerial 518000, China vehicles (UAV). New applications put forward higher State Key Laboratory of Functional Materials for requirements for detecting parameters of a two- Informatics, Shanghai Institute of Microsystem and dimensional (2-D) gas-flow vector over a full range of Information Technology, Chinese Academy of Sciences, 360¼. A novel thermal flow sensor on Si/SiO2/Pt/AlN Shanghai 200050, China substrate is presented to optimize sensor Photonics Research parameters. Eight thermal elements patterned as https://doi.org/10.1364/PRJ.7.001127 equally divided sectors of a regular octagon compose the sensor probe. Dual coordinate systems are With the increasing demand for high integration and created based on the regular octagon distribution to multi-color photodetection for both military and realize the self examined function. The longitudinal civilian applications, the research of multi- heat conduction mode shortens the heat transfer wavelength detectors has become a new research distance from mm level to micron level. And the a- hotspot. However, current research has been mainly axis oriented AlN film improves the heat transfer in visible dual- or multi-wavelength detectors, while efficiency due to its high thermal conductivity. Dual integration of both visible light and ultraviolet (UV) coordinate self examined method is proven through dual-wavelength detectors has rarely been studied. In experiments for the first time. Measurement results this work, large-scale and high-quality monolayer show that the maximum measurement flow velocity MoS2 was grown by the chemical vapor deposition is up to 37m/s, with an output voltage sensitivity of method on transparent free-standing GaN substrate. 28.1 mV/ (m/s). Flow direction was measured over a Monolithic integration of MoS2-based visible full range of 360¼ with an accuracy of 0.5 m/s at low detectors and GaN-based UV detectors was velocity and 5% at high velocity. We believe that the demonstrated using common semiconductor sensor presented in this work will pave the way for fabrication technologies such as photolithography, novel applications in calorimetric sensors and array argon plasma etching, and metal deposition. High sensors. performance of a 280 nm and 405 nm dual-

GaNEX | III-N Technology Newsletter No. 81 | 30

High-performance room-temperature TiO2- the excellent narrow band UV sensitivity, the device functionalized GaN nanowire gas sensors also demonstrated a large linear dynamic range of 71 Department of Electrical and Computer Engineering, decibels (dB) and a fast photoresponse speed (a rise George Mason University, Fairfax, Virginia 22030, USA time of 0.75 μs and a fall time of 0.91 μs). The Department of Electrical and Electronics Engineering, excellent performance is attributed to excellent George Washington University, Washington, DC 2001, USA carrier separation efficiency at the heterojunction N5 Sensors, Inc., Rockville, Maryland 20850, USA interface and improved carrier collection efficiency

through the multi-walled carbon nanotube (MWCNT) Applied Physics Letters https://doi.org/10.1063/1.5116677 network. All the above advantages are of great importance for commercial deployment of Hybrid gas sensors based on TiO2 functionalized perovskite-based photodetectors. gallium nitride nanowires have been prepared by nanofabrication and comprehensively studied for Two-terminal terahertz detectors based on high-responsivity applications. The devices exhibited AlGaN/GaN high-electron-mobility transistors a high responsivity (25%) to 500 ppm NO2 assisted Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO), with ultraviolet illumination at room temperature. Chinese Academy of Sciences, 398 Ruoshui Road, Suzhou The thickness and doping concentration of TiO2 were 215123, People's Republic of China engineered to improve the transducer function. The School of Nano Technology and Nano Bionics, University of result indicated that an excellent n-type response can Science and Technology of China, Suzhou 215123, People's be stably obtained for a doping range from Republic of China 1 × 1017 cm−3 to 1 × 1019 cm−3. The TiO2 thickness College of Electronic and Information Engineering, Suzhou and doping concentration can be further fine-tuned University of Sciences and Technology, Suzhou 215009, to achieve optimal performance. In addition, a People's Republic of China comprehensive device simulation was carried out to Kotelnikov Institute of Radio Engineering and Electronics, understand the device operation and gain insight for Saratov Branch, Russian Academy of Sciences, Saratov 410019, Russia optimizing the device performance.

Applied Physics Letters Inorganic vacancy-ordered perovskite https://doi.org/10.1063/1.5114682 Cs2SnCl6:Bi/GaN heterojunction photodiode for narrowband, visible-blind UV detection We report an approach to make two-terminal Electrical, Computer, and Systems Engineering antenna-coupled AlGaN/GaN high-electron-mobility- Department, Rensselaer Polytechnic Institute, Troy, New transistor self-mixing terahertz detectors. Fluorine York 12180, USA ion implantation is used to increase the threshold Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New voltage of the AlGaN/GaN two-dimensional electron York 12180, USA gas. An optimal implantation dose can be reached so that the detector responsivity is maximized at zero Applied Physics Letters gate voltage or with the gate floating. The https://doi.org/10.1063/1.5123226 relationship between the ion dosage and the threshold voltage, electron mobility, electron density, A heterojunction photodiode was fabricated from Bi responsivity, and noise-equivalent power (NEP) is doped Cs2SnCl6 nanoparticles (Cs2SnCl6:Bi NPs) spin- obtained. A minimum optical NEP of coated on an epitaxially grown GaN substrate. With 47 pW/Hz⎯⎯⎯⎯⎯√ is achieved from a two-terminal the back illumination configuration, the detector at 0.65 THz. The capability of two-terminal heterojunction photodiode demonstrated excellent operation allows for the design of a large array of narrow-band UV sensing capability with a full antenna-coupled high-electron-mobility transistor wavelength of half maximum of 18 nm and a detectors without the demanding needs of routing maximum detectivity of 1.2 × 1012 jones, which is negative gate voltage lines around the antenna array promising for biomedical applications. In addition to and minimizing the gate leakage current.

GaNEX | III-N Technology Newsletter No. 81 | 31

Low operating temperature NO gas sensors based based p-i-n ultraviolet photodetectors (PDs). The cut- hydrogen peroxide treated GaN nanorods off wavelengths of the PDs grown on normal sapphire Department of Physics, Chungnam National University, substrates (NSSs) and on patterned sapphire Daejeon, 34134, Republic of Korea substrates (PSSs) were 445 and 450 nm, respectively, Department of Information and Communications, Joongbu which is consistent with the photoluminescence University, 305 Donghen-ro, Goyang, Kyunggi-do, 10279, emission wavelength. From the crystal and optical Republic of Korea analyses, we found that the crystallinity and the

absorption of the PDs grown on PSSs were superior Physica E: Low-dimensional Systems and Nanostructures https://doi.org/10.1016/j.physe.2019.113725 to those of the PDs grown on NSSs. The maximum photoreactivities of the PDs grown on PSSs and on In recent days, surface treatment strategies have NSSs were 0.176 A/W and 0.109 A/W, respectively. In employed to enhance the active sites for addition, the external quantum efficiencies of those chemisorption of gas molecules. In this work, the PDs were 56.1% and 34.8%, respectively. From these simple and effective hydrogen peroxide (H2O2) results, we suggest that a PSS can play an important treatment is used to enhance the active sites on the role in achieving a high reactivity and external surface of gallium nitride (GaN) nanorods (NRs) for quantum efficiency for InGaN-based PDs due to nitric oxide (NO) gas detection. The surface improved crystallinity and decreased optical treatment was carried out by immersing the GaN NRs absorption in the sapphire substrate. into a hydrogen peroxide (H2O2) solution at different temperatures for 10 min. The X-ray photoelectron Perspectives in the Development of Biosensors spectroscopy (XPS) is used to find the Based on AlGaN/GaN HEMT physicochemical properties of GaN NRs. XPS studies Bauman Moscow State Technical University, Moscow, revealed that the active sites (O2 species) on GaN Russia Peoples’ Friendship University of Russia, Moscow, Russia NRs were increased by H2O2 treatment. NO gas Saint Petersburg Electrotechnical University “LETI”, St. sensing measurements revealed that response of the Petersburg, Russia H2O2 treated GaN NRs enhanced by 4-times than Russian Medical Academy of Postgraduate that of pristine GaN NRs to 100 ppm of NO gas EducationMinistry of Health of the Russian Federation, concentration at 50 °C. Further, H2O2 treated GaN Moscow, Russia NRs exhibited high response under UV illuminations Federal Research and Clinical Center for Physical-and- (λ = 382 nm, P = 1.45 mW/cm2) compared to dark Chemical MedicineFederal Medical and Biological Agency, conditions. Under UV illumination, the H2O2 treated Moscow, Russia GaN NRs generated a large amount of electron-hole pairs, indicating additional defect states on the Biomedical Engineering https://doi.org/10.1007/s10527-019-09908-x surface of GaN NRs induced by the H2O2 treatment and these are accountable for the high NO gas The development and investigation of biosensors for response. the early and rapid diagnosis of a wide spectrum of

diseases to provide significant reductions in mortality Effect of a Patterned Sapphire Substrate on InGaN- and loss of working time as a result of timely Based p-i-n Ultraviolet Photodetectors treatment is a current challenge in many countries. Department of Nano-Optical EngineeringKorea Polytechnic University, Siheung, Korea The active progress in biosensor technology is Department of Materials Science and Engineering, Daejin promoted by the fact that it is an interdisciplinary University, Pocheon, Korea field exploiting advancements in very diverse areas of knowledge: from physiology to nanotechnology and Journal of the Korean Physical Society electronics. https://doi.org/10.3938/jkps.75.362

InGaN/GaN multi-quantum well (MQW) structures were used as an intrinsic semiconductor in InGaN-

GaNEX | III-N Technology Newsletter No. 81 | 32

Analysis of Current–Voltage Characteristics in UV membrane while SV only contains the information of AlGaN Heterostructure FPAs the sensitive membrane, which helps us to analyze JSC R&P Association Orion, Moscow, Russia the device performance. In this paper, the sensitivity Moscow Institute of Physics and Technology, Dolgoprudny, SA was deduced theoretically based on the previous Russia research and was verified experimentally. On this basis, we put forward a method that can separate the Journal of Communications Technology and Electronics effect of the sensitive membrane on the sensitivity https://doi.org/10.1134/S106422691909016X from the material completely by designing a series of UV visible-blind and solar-blind 320 × 256 photodiode AlGaN/GaN based heterostructure ISFET pH sensors arrays based on AlxGa1 – xN heteroepitaxial with different sizes of the channel area (width/length structures (AlGaN HES) and sensitive in the near- parameter). Experimental result shows the ultraviolet range of 0.2–0.4 μm have been created importance of this method in the future research. and studied. The AlGaN HES were grown by organometallic vapor deposition (MOCVD) and molecular beam epitaxy (MBE) on sapphire substrates. To reduce structural defects, the state of the surface and the surface layer of epipolished sapphire substrates was investigated, and a finishing technology was developed. UV FPAs in the AlGaN HES were produced by ion etching. The dark current components for AlGaN photodiodes were simulated. The main dark current components, such as generation–recombination, shunting leakage, hopping conductivity, and Poole–Frenkel components, are calculated. The possibility of achieving photoelectric parameters on the level of the best foreign counterparts is demonstrated.

Analysis and experiment of the sensitivity of AlGaN/GaN based heterostructure all-solid-state pH sensor School of Electronics and Information Technology, Sun Yat- sen University, Guangzhou 510006, P. R. China State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou 510275, P. R. China

AIP Advances https://doi.org/10.1063/1.5094584

Ion-sensitive field effect transistor (ISFET) has been widely used as a pH sensor. Its sensitivity can be expressed in terms of current or voltage which were defined by us as SA and SV in this article. Using current to represent sensitivity is more convenient for it can simplify the subsequent circuits. What’s more, SA contains more information including the geometry of the device, the parameter of the epitaxial material and the property of the sensitive

GaNEX | III-N Technology Newsletter No. 81 | 33

GROUP 6 - Photovoltaics and Energy harvesting Group leader: Eva Monroy (INAC-CEA) Information selected by Knowmade

Enhanced charge separation and interfacial charge based photoelectrode to readily enhance the PEC transfer of InGaN nanorods/C3N4 heterojunction performance. photoanode State Key Laboratory of Luminescent Materials and Effect of light wavelengths on the non-polar InGaN- Devices, South China University of Technology, Guangzhou, based thin film solar cells performances using one- 510640, China dimensional modeling Engineering Research Center on Solid-State Lighting and its Applied Materials Laboratory (AML), University of Djilali Informationisation of Guangdong Province, South China Liabes, 22000, Sidi Bel Abbès, Algeria University of Technology, Guangzhou, 510640, China Electronic Department, Faculty of Technology, University Department of Electronic Materials, School of Materials M. Boudiaf, 28000, Msila, Algeria Science and Engineering, South China University of Inorganic Materials Laboratory, University M. Boudiaf, Technology, Guangzhou, 510640, China 28000, Msila, Algeria Tianjin Institute of Power Sources, Tianjin, 300384, China Laboratory of Materials Physics and its Applications,

University of M'sila, 28000 M'sila, Algeria Electrochimica Acta https://doi.org/10.1016/j.electacta.2019.134844 Journal of Science: Advanced Materials and Devices

https://doi.org/10.1016/j.jsamd.2019.08.008 Semiconducting heterostructures designed with rational engineering of energy bands and interfaces In the present contribution, we determine the effect can accelerate electron-hole separation to boost of light wavelength variation on the performances of photoelectrochemical (PEC) water splitting. Herein, the non-polar InGaN-based solar cells in order to find InGaN nanorods (NRs)/C3N4 heterojunction the optimum light wavelength that yields a high photoanode has been constructed by directly loading efficiency. The calculations are performed using one- C3N4 on the InGaN NRs surface through a simple dimensional SCAPS-1D tool (One-Dimensional Solar chemical vapor deposition method. The working Cell Capacitance Simulator). The simulation has been principles and interfacial charge kinetics of the carried out by lighting through n-In0.3Ga0.7As layer. heterojunction have been proposed. The unique An efficiency of 12.24% with FF = 51.35%, VOC = 0.72 heterojunction exhibits efficient charge separation Volt and JSC = 32.80 mA/cm2 is obtained under through the potential gradient and enhanced AM1.5G illumination. The quantum efficiency interfacial charge transfer due to the surface characteristic displays a maximum value of more than passivation. Eventually, the photocurrent density of 90% in the visible range using AM1.5G illumination. the InGaN NRs/C3N4 heterojunction photoanode Moreover, our results show that with increasing the with loading weight ratio of 0.38% reaches up to light wavelengths from the blue light (around 450 13.9 mA/cm2 at 1.23 V vs. RHE under an illumination nm) to the end of the red light (around 700 nm), the of ∼100 mW/cm2, which is 2 times higher than that efficiency increases from 13.76% to above of 20%. of the pristine InGaN NRs. The applied bias photon- The short-circuit current density is also increased to-current efficiency of the designed heterojunction from 37.33 mA/cm2 to 53.81 mA/cm2 with increasing can achieve as high as 2.26% at 0.9 V vs. RHE, 1.65 the light wavelengths from 450 nm to 700 nm. times higher than the bare InGaN NRs (1.37%). However, the variation of the light wavelength seems Moreover, the InGaN NRs/C3N4 heterojunction to have only a small influence on the open-circuit exhibits an obviously improved stability against voltage and fill-factor. The present study provides photocorrosion due to the efficient interfacial charge information about the properties of the materials transfer. This work can open up a novel route for the used in the cell structure for efficient InGaN solar rational design and construction of heterojunction cells.

GaNEX | III-N Technology Newsletter No. 81 | 34

Theoretical prediction of two-dimensional ZnO/GaN hydrogen evolution reaction (HER). The synthesized van der Waals heterostructure as a photocatalyst Pt/PGaN electrode showed excellent catalytic for water splitting performances for HER with an overpotential of 98 mV School of Mechanical Engineering, Southeast University, at 10 mA/cm2, a Tafel slope of 85 mV/dec and an Nanjing, Jiangsu 211189, China outstanding stability. Furthermore, this work may School of Materials Science and Engineering, Southeast provide a concept to prepare a dual function University, Nanjing, Jiangsu 211189, China electrode for both electrochemical and

photoelectrochemical water splitting. Chemical Physics https://doi.org/10.1016/j.chemphys.2019.110539 Negative electron affinity driven broadband In this work, based on density functional calculations, absorption of Cs3+nPbnSb2I9+3n/GaN van der the structural, electronic, interfacial and optical Waals heterostructures† performances of the two-dimensional van der Waals Department of Physics, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, P. R. (vdW) heterostructure formed by ZnO and GaN are China addressed. The heterostructure possesses a type-II Collaborative Innovation Center of Advanced band structure and decent band edge positions which Microstructures, Nanjing University, Nanjing 210093, P. R. can separate the photogenerated electron–holes China pairs constantly for redox reaction of the water College of Optical and Electronic Technology, China Jiliang splitting at pH 0 and 7. The charge-density difference University, 310018 Hangzhou, China and potential drop across the interface of the First-class Discipline sans and High-level University heterostructure are investigated, which can result a Construction Office, Nanjing University of Posts and built-in electric field to prevent the recombination of Telecommunications, Nanjing 210023, P. R. China the photogenerated electron–holes. Besides, the high College of Physical Science and Technology, Nanjing Normal University, Nanjing 210023, P. R. China mobility of electrons about 3004.49 cm2·V–1·s–1 is found in the heterostructure along the transport Journal of Materials Chemistry A direction. The heterostructure also has excellent https://doi.org/10.1039/C9TA08458D optical absorption performance, which can be mediated by the external strain. This study offers Metal halide perovskites (MHPs) with highly sensitive guidelines for the design of vdW heterostructures photoelectric response and ultrahigh absorption used as photocatalysts for water splitting. coefficient in the visible range exhibit huge potential as building blocks for optoelectronic devices. Electrodeposition of platinum nanoparticles onto However, these perovskites suffer from poor porous GaN as a binder-free electrode for hydrogen absorption efficiency in the infrared range due to the evolution reaction weak coupling of infrared light. In this work, we School of Nano Technology and Nano Bionics, University of report a new class of MHP-based heterostructures by Science and Technology of China, 230026 Hefei, P. R. China the integration of two-dimensional Division of Interdisciplinary Research, Suzhou Institute of Cs3+nPbnSb2I9+3n perovskites with GaN nanosheets Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, 215123 Suzhou, P. R. China for the realization of highly efficient carrier separation and broadband absorption. We find that Chemical Physics Letters the formation of the Cs/GaN(0001) interface in https://doi.org/10.1016/j.cplett.2019.136796 Cs3+nPbnSb2I9+3n/GaN heterostructures can induce the shift of the vacuum level below the conduction Electrochemical water splitting has been recognized band minimum, resulting in negative electron affinity as a sustainable and clean method to produce (NEA). Moreover, the NEA of the heterostructures is hydrogen. Herein, we report the electrodeposition of not sensitive to the thickness of perovskite and GaN platinum nanoparticles (PtNPs) onto porous GaN layers. Owing to the type-II band alignment and NEA (PGaN) electrode obtained by photoelectrochemical of these heterostructures, they exhibit highly efficient etching planar GaN as a binder-free electrode for carrier separation and enhanced optical absorption

GaNEX | III-N Technology Newsletter No. 81 | 35 from the infrared to ultraviolet light region, which potential, it is critical to enhance the plasmon excited result in maximum power conversion efficiency as hot carrier transfer and collection. However, the lack high as 28.5%. The findings suggest the large of atomistic understanding of the carrier transfer potential of Cs3+nPbnSb2I9+3n/GaN across the interface, especially when the carrier is still heterostructures for optoelectronic applications, such "hot", makes it challenging to design more efficient as solar cells, photodetectors, and field emission system. In this work, we apply the non-adiabatic devices. molecular dynamics simulation to study hot carrier dynamics in the system of Au nanocluster on top of

GaN surface. By setting up the initial excited hole in Modeling the impact of temperature effect and Au, the carrier transfer from Au to GaN is found to be polarization phenomenon on InGaN/GaN-Multi- on a sub-pico second time scale. The hot hole first quantum well solar cells cools to the band edge of Au d-states while it Quantum and Statistical Physics Laboratory, Faculty of transfers to GaN. After the hole has cooled down to Sciences of Monastir, University of Monastir, Monastir the band edge of GaN, we find some of the charges 5019, Tunisia can return back to Au. By applying different external LaMCScI, Group of Optoelectronic of Semiconductors and potentials to mimic the Schottky-barrier band Nanomaterials, ENSET, Mohammed V University in Rabat, bending, the returning charge can be reduced, Morocco demonstrating the importance of the internal electric Department of Computer Science and Information, College field. Finally, with the understanding of the carrier of Science, Majmaah University, Zulfi 11932, Saudi Arabia transfer's pathway, we suggest that a ZnO layer Université de Lorraine, LCP-A2MC, F-57000, Metz, France between GaN and Au can effectively block the "cold" Department of Physics, College of Science, Majmaah University, Al Zulfi 11932, Saudi Arabia carrier from returning back to Au but still allow the Electronics and Microelectronics Laboratory, Faculty of hot carrier to transfer from Au to GaN. Science of Monastir, University of Monastir, Monastir 5019, Tunisia Evaluating the performance of InGaN/GaN multi- quantum-well solar cells operated at elevated Optik temperatures via DC and small-signal AC analysis https://doi.org/10.1016/j.ijleo.2019.163385 Georgia Institute of Technology, Atlanta, GA 30332, United States of America Taking into consideration the effects of electronic Arizona State University, Tempe, AZ 85281, United States properties (and their behavior under temperature), of America we present a new numerical model for the PhotoNitride Devices Inc., Tempe, AZ 85284, United States determination of the characteristic parameters of the of America InGaN/GaN multiple quantum well solar cells. Our Japanese Journal of Applied Physics approach shows that it is possible to enhance the https://doi.org/10.7567/1347-4065/ab3b66 performance of the InGaN/GaN MQW by tuning the electronic properties and by introducing the impact InGaN/GaN multi-quantum-well (MQW) solar cells of the polarization of heterostructures with N-face are investigated with temperature-dependent DC and and for an optimal indium composition. AC analysis, and the effects of differing QW number and thickness are determined. The carrier transport is Ultrafast Hot Carrier Injection in Au/GaN: The Role shown to be dominated by thermionic emission of Band Bending and the Interface Band Structure rather than tunneling at elevated temperature but Joint Center for Artificial Photosynthesis and Materials limited by recombination outside the depletion Sciences Division, Lawrence Berkeley National Laboratory, region. Temperature-dependent AC parameters of Berkeley, California 94720, USA the III-N MQW devices in high-level injection are J. Phys. Chem. Lett. determined through a refined AC circuit model of the https://doi.org/10.1021/acs.jpclett.9b02402 device. It is shown that the use of AC small-signal analysis and its ability to extract stored charge in the Plasmon photochemistry can potentially play a QWs, the comparison of built-in potential to V OC, significant role in photocatalysis. To realize this and other solar cell critical values allows a device

GaNEX | III-N Technology Newsletter No. 81 | 36 designer insight not possible via DC analysis alone. the operational temperature of a given high This critical data suggests that the number of QWs temperature solar cell. and total depletion volume needs to be matched to

GaNEX | III-N Technology Newsletter No. 81 | 37

GROUP 7 - Materials, Technology and Fundamental Group leader: Jean-Christophe Harmand (LPN-CNRS)

NANO Surface and dislocation investigation of planar Information selected by GaN formed by crystal reformation of nanowire Jesús Zúñiga Pérez (CRHEA-CNRS) arrays Synchrotron Radiation Research and NanoLund, Lund Understanding the p-type GaN nanocrystals on University, Box 118, 221 00, Lund, Sweden InGaN nanowire heterostructures Glo AB, Ideon Science Park, Scheelevägen 22, S-223 63 Optic & Electronic Component Material Center, Korea Lund, Sweden Institute of Ceramic Engineering & Technology, Jinju Centre for Analysis and Synthesis and NanoLund, Lund 52851, Republic of Korea University, Box 124, 221 00 Lund, Sweden School of Advanced Materials Engineering, Engineering RISE Research Institutes of Sweden, Scheelevägen 17, S- College, Chonbuk National University, Deokjin-dong 664- 223 70, Lund, Sweden 14, Jeonju 561-756, Republic of Korea Solid State Physics and NanoLund, Lund University, Box 118, 221 00 Lund, Sweden ACS Photonics Hexagem AB, Ideon Science Park, Scheelevägen 15, S-223 https://doi.org/10.1021/acsphotonics.9b01035 70 Lund, Sweden

The efficiency of semiconductor light-emitting PHYSICAL REVIEW MATERIALS diode has been largely limited by the extremely https://doi.org/10.1103/PhysRevMaterials.3.093604 inefficient p-type conduction on InGaN heterostructures. Here, we report highly efficient p- In this paper we present a process of forming type GaN nanocrystals fabricated by p-i-n nanowire monolithic GaN surface from an ordered nanowire heterostructures using selective area epitaxial array by means of material redistribution. This growth (SAG). With the different Mg-doping growth process, referred to as reformation, is performed in conditions in the p-GaN nanostructure, different a conventional MOVPE crystal growth system with structure formations and various Mg incorporations the gallium supply turned off and allows a crystal were confirmed by detailed scanning electron nanostructure to change shape according to microscopy (SEM) and cathodoluminescence (CL) differences in surface energies between its facets. analysis. The growth mechanism of p-GaN Using reformation, coalescence may proceed closer nanocrystal formation on nanowire structures was to thermodynamic equilibrium, which is required also suggested by CL mapping measurements. for fabrication of high-quality substrate material. Single nanowire light-emitting diodes (LEDs) Scanning probe techniques are utilized, exhibited different current−voltage (I−V) behaviors complemented by cathodoluminescence and from various p-GaN nanocrystal formations. The electron microscopy, to investigate structural and resulting p-contacted InGaN/GaN nanowire LEDs electrical properties of the surface after showed a low turn-on voltage (∼2.3 V), reduced reformation, as well as to assess densities, location, resistance, and enhanced electroluminescence (EL) and formation of different types of defects in the intensity at 532 nm wavelength, which is very GaN film. Spatial variations in material properties important to realize high efficiency InGaN LEDs such as intrinsic majority-carrier types can be operating in the green and red wavelength ranges. attributed to the radical changes in growth This demonstration provides important insight on conditions required for sequential transition the fundamental formation characteristics of p-GaN between nanowire growth, selective shell growth, nanocrystals on the nanowire heterostructure and and reformation. These properties enable us to also offers a viable path to realize multi-functional assess the impact of the process on densities, nano-scale photonic and electronic devices. locations, and formation of different types of dislocations in the GaN film. We find a fraction of the nanowires to comprise of a single electrically

GaNEX | III-N Technology Newsletter No. 81 | 38 neutral edge dislocation, propagating from the GaN boundaries can be avoided, and threading buffer, while electrically active dislocations are dislocations can be annihilated. It is believed that found at coalesced interfaces between nanowires. microscale materials are predominant masks for By decreasing the mask aperture size and changing SAG, and nanoselective area growth (NSAG) the nucleation conditions the prevalence of technology is more superior, which may allow nanowires comprising edge dislocation was epilayer mechanical exfoliation from substrate. significantly reduced from 6% to 3%, while the Here we demonstrate fabrication of architectural density of interface dislocations was reduced from GaN nanostructures by self-assembly NSAG (SNSAG) 6×108 to 4×107cm−2. Using a sequential technology using multilayer graphene (MLG) as a reformation process was found to create inversion nanomask. The microstructure and optical domains with low surface potential N-polar regions properties, measured by scanning electron in an otherwise Ga-polar GaN film. The inversion microscopy, transmission electron microscopy, domains were associated with pinned dislocation cathodeluminescence, micro-Raman, and micro- pairs, and were further confirmed by selective wet photoluminescence, were characterized for etching in NaOH. This lateral polarity inversion was evidencing the high-quality GaN nanostructures. thoroughly eliminated in samples formed by a Moreover, high-quality, stress-relaxation GaN films continuous reformation process. These results were SNSAG on MLG/SiC and mechanically reveal a path and challenges for growing GaN exfoliated from substrates for obtaining free- substrates of superior crystal quality through standing GaN. This technique enables integration of nanowire reformation. any nonplanar and planar semiconductor materials with graphene for the extensible application. Self-assembly graphene nanomask for epitaxial growth of nonplanar and planar GaN Suzhou Institute of Nano-Tech and Nano-Bionics NON POLAR / SEMI POLAR (SINANO), Chinese Academy of Sciences (CAS), Suzhou Information selected by 215123, People’s Republic of China Knowmade Suzhou Nanowin Science and Technology Co., Ltd., Suzhou 215123, People’s Republic of China Effect of light wavelengths on the non-polar School of Optoelectronic Science and Engineering & InGaN-based thin film solar cells performances Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215006, using one-dimensional modeling People’s Republic of China Applied Materials Laboratory (AML), University of Djilali Key Lab of Advanced Optical Manufacturing Technologies Liabes, 22000, Sidi Bel Abbès, Algeria of Jiangsu Province & Key Lab of Modern Optical Electronic Department, Faculty of Technology, University Technologies of Education Ministry of China, Soochow M. Boudiaf, 28000, Msila, Algeria University, Suzhou 215006, People’s Republic of China Inorganic Materials Laboratory, University M. Boudiaf, 28000, Msila, Algeria CrystEngComm Laboratory of Materials Physics and its Applications, https://doi.org/10.1039/C9CE00970A University of M'sila, 28000 M'sila, Algeria

Taking advantage of the unique properties of two- Journal of Science: Advanced Materials and Devices https://doi.org/10.1016/j.jsamd.2019.08.008 dimensional (2D) materials, van der Waals epitaxy or remote epitaxy of nonplanar and planar In the present contribution, we determine the materials on 2D materials plays an important role in effect of light wavelength variation on the the application, but is often limited by low performances of the non-polar InGaN-based solar crystalline quality with misorientation in nonplanar cells in order to find the optimum light wavelength materials, or grain boundaries and high threading that yields a high efficiency. The calculations are dislocation densities in planar materials. Selective performed using one-dimensional SCAPS-1D tool area growth (SAG) is an effective way to break the (One-Dimensional Solar Cell Capacitance Simulator). limitation, in which orientation is concordant, grain The simulation has been carried out by lighting

GaNEX | III-N Technology Newsletter No. 81 | 39 through n-In0.3Ga0.7As layer. An efficiency of the AlN/sapphire interface. Such phenomenon was 12.24% with FF = 51.35%, VOC = 0.72 Volt and JSC = found to have a positive impact towards 32.80 mA/cm2 is obtained under AM1.5G accumulating the propagation of defects. The illumination. The quantum efficiency characteristic surface morphology analysis elucidates the reduced displays a maximum value of more than 90% in the stripe-like undulations, whereby the terrace-like visible range using AM1.5G illumination. Moreover, features in the lower scales endured an enhanced our results show that with increasing the light rearrangement favoring the reduced defect density. wavelengths from the blue light (around 450 nm) to the end of the red light (around 700 nm), the efficiency increases from 13.76% to above of 20%. MATERIAL / CHARACTERIZATION / The short-circuit current density is also increased EQUIPMENT / NUMERICAL SIMULATION from 37.33 mA/cm2 to 53.81 mA/cm2 with Information selected by increasing the light wavelengths from 450 nm to Agnès Trassoudaine (Université d'Auvergne), Yvon Cordier and Mathieu Leroux (CRHEA-CNRS) 700 nm. However, the variation of the light wavelength seems to have only a small influence on Lattice-matched GaN(0002)/LSAT(111) hetero- the open-circuit voltage and fill-factor. The present structures grown by PLD and analyzed by first- study provides information about the properties of principles calculations the materials used in the cell structure for efficient State Key Laboratory of Luminescent Materials and InGaN solar cells. Devices, South China University of Technology, Guangzhou 510640, People's Republic of China Impact of Strained Periodic Multilayer on the Engineering Research Center on Solid-State Lighting and Surface and Crystal Quality of Semi-polar (11-22) its Informationisation of Guangdong Province, South GaN Template China University of Technology, Guangzhou 510640, Low Dimensional Materials Research Centre, People's Republic of China Department of Physics, Faculty of Science, University Department of Electronic Materials, School of Materials of Malaya, 50603 Kuala Lumpur, Malaysia Science and Engineering, South China University of Materials Department, University of California, Santa Technology, Guangzhou 510640, People's Republic of Barbara, United States China

Cryst. Growth Des. Japanese Journal of Applied Physics https://doi.org/10.1021/acs.cgd.9b00206 https://doi.org/10.7567/1347-4065/ab354c

Efficient reduction of defects and dislocations in La0.3Sr1.7AlTaO6(LSAT), a desired substrate for semi-polar (11-22) GaN epilayer with the use of GaN epitaxial growth with a lattice mismatch as AlN/GaN strained periodic multilayer is small as 1%, has not been applied in growth of GaN demonstrated. On- and off-axis x-ray rocking curve films due to hetero-interface rotation in epitaxial analyses have shown significant improvement in the growth. In this paper, high-quality GaN epitaxial crystalline qualities with remarkable narrowing in films with a small FWHM for GaN(0002) X-ray their respective full width at half maximum upon rocking curve of 0.06° have been grown by pulsed utilization of increased AlN/GaN pairs. X-ray laser deposition (PLD) with a lattice mismatch as reciprocal space mapping revealed a prominent small as 1% between GaN and LSAT, and the increment in the degree of relaxation state, with corresponding mechanism avoiding interface notable shrinkage in the diffuse scattering streak. rotation has also been investigated by first- Structural evaluation via transmission electron principles calculation. On the one hand, we found microscope illuminates the interruption of defect that GaN grown on LSAT by PLD shows an in-plane and dislocation propagation due to the strained relationship of GaN[2-1-10]//LSAT[1-10], revealing a periodic multilayers. It was observed that the first small lattice mismatch of 1%. On the other hand, 20th pairs exhibited a three dimensional growth the first-principles calculation based on density mode owning to numerous defects originating from function theory reveals that GaN growth along

GaNEX | III-N Technology Newsletter No. 81 | 40

GaN[2-1-10]//LSAT[1-10] shows a higher interface nitrogen at the molten Ga - substrate interface energy barrier compared with that along GaN[1- allows for liquid phase epitaxy. 100]//LSAT[1-10] with a lattice mismatch of 12.5%. The high interface energy barrier can only be Evidence of a strong perpendicular magnetic provided by PLD. Moreover, this work is of anisotropy in Au/Co/MgO/GaN heterostructures paramount importance for understanding the School of Nano Technology and Nano Bionics, University hetero-interface formation mechanism in a of Science and Technology of China, 96 Jinzhai Road, GaN/substrates system and will be beneficial to the Baohe, Hefei 230026, P.R.China development of GaN-based devices that require Université de Lorraine, CNRS, Institut Jean Lamour, UMR 7198, campus ARTEM, 2 Allée André Guinier, 54011 high-quality GaN epitaxial films. Nancy, France

Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Liquid Phase Epitaxy of Gallium Nitride Academy of Sciences, 215123, Suzhou, P.R.China Department of Chemical Engineering, University of Key Laboratory of Magnetic Materials and Devices, Louisville, Louisville, Kentucky 40292 Ningbo Institute of Materials Technology and Conn Center for Renewable Energy Research, University Engineering, Chinese Academy of Sciences, Ningbo of Louisville, Louisville, Kentucky 40292 315201, P.R.China CEA LETI, 17 rue des Martyrs, F-38054 Grenoble, France Cryst. Growth Des. School of Physics, Peking University, 100871, Beijing, https://doi.org/10.1021/acs.cgd.9b01011 P.R.China

In this work, liquid phase epitaxy of gallium nitride Nanoscale Advances (GaN) has been achieved using pulsed plasma https://doi.org/10.1039/C9NA00340A nitridation of molten Ga films. Typically, continuous exposure of Ga to nitrogen plasma results in the We report a strong perpendicular magnetic formation of a thick GaN crust that prevents the anisotropy (PMA) in Au/Co/MgO/GaN growth of GaN layers on GaN seeds or GaN-on- heterostructures from both experiments and first- sapphire substrates. The GaN crust formation on principles calculations. The Au/Co/MgO molten Ga is a consequence of a high concentration heterostructures have been grown by molecular of dissolved nitrogen at the top surface of molten beam epitaxy (MBE) on GaN/sapphire substrates. Ga layers. Here, we present a concept of using By carefully optimizing the growth conditions, we pulsed sequence (on and off time scales) for obtained a fully epitaxial structure with crystalline controlling the concentration of nitrogen inside the orientation relationship Au(111)[-110]// melt and enabling growth at the molten Ga- Co(0001)[11-20]// MgO(111)[10-1] //GaN(0002)[11- substrate interface. Results showed that the 20]. More interesting, we demonstrate that a 4.6 technique allows for epitaxial growth on homo- nm thick Co film grown on MgO/GaN still exhibits a substrates and promotes the growth of additional large perpendicular magnetic anisotropy. First- layers on the pre-existing seeds. High resolution principles calculations performed on the Co transmission electron microscopy (HRTEM) (4ML)/MgO(111) structure showed that the characterization confirmed epitaxial growth of GaN. MgO(111) surface can strongly enhance the A mass transport model was developed to discuss magnetic anisotropy energy by 40% compared to a the effect of bulk recombination, diffusion, and reference 4ML thick Co hcp film. Our layer-resolved pulsing in the concentration of nitrogen into the and orbital-hybridization resolved anisotropy molten Ga. Results indicated that pulsing favored analyses helped to clarify that the origin of the PMA both the recombination of radicals in the bulk and enhancement is due to the interfacial hybridization the diffusion of species into the metal compared to of O 2p and Co 3d orbitals at the Co/MgO interface. the dissolution of radicals. As a result, the The perpendicularly magnetized Au/Co/MgO/GaN concentration of nitrogen at the surface of the heterostructures are promising for efficient spin metal is decreased, while the concentration of injection and detection in GaN based opto- electronics without any external magnetic field.

GaNEX | III-N Technology Newsletter No. 81 | 41

Migration of carbon from Ga sites to N sites in extracted barrier heights and ideality factors is GaN: a combined PAS and hybrid DFT study described as a consequence of lateral State Key Laboratory of Artificial Microstructure and inhomogeneity at the metal-semiconductor (M-S) Mesoscopic Physics, School of Physics, Peking University, interface. It is shown that by invoking a modified Beijing 100871, People's Republic of China log-normal distribution of barrier heights at the M-S Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese interface, the extracted barrier height temperature Academy of Sciences, Suzhou 215123, People's Republic dependence can be well explained. Further, it is of China shown that this approach can describe the voltage College of Materials Science and Engineering, Chongqing University, Chongqing 400044, People's Republic of dependence of the lateral barrier distribution China revealing that for effective barrier height values Key Laboratory of Nuclear Analysis Techniques, Institute calculated at increasingly higher voltages, the of High Energy Physics, Chinese Academy of Sciences, distribution begins to converge on a single value of Beijing 100049, People's Republic of China 0.77 eV. This value is in good agreement with the Collaborative Innovation Center of Quantum Matter, flat-band barrier height of 0.77 ± 0.02 eV extracted Beijing 100871, People's Republic of China from capacitance-voltage (C-V) measurements on the same device. The same procedure is used to Japanese Journal of Applied Physics describe the parallel conduction path apparent at https://doi.org/10.7567/1347-4065/ab3548 low temperatures, revealing its behavior is

Carbon (C) is of great importance to realize semi- indicative of an additional Schottky region with an insulating gallium nitride (GaN) for power electronic increased density of low barriers which are more devices. We demonstrate that C can migrate from heavily perturbed by external bias. Finally, the Ga sites to N sites after high temperature annealing model is successfully applied to previously of C doped GaN. The migration process is revealed published work on various Schottky diodes through the observation of the generated Ga structures. vacancies-related defects after annealing by positron annihilation spectroscopy. The activation V-shaped dislocations in a GaN epitaxial layer on energy of this migration process is estimated to be GaN substrate Institute of Materials and Systems for Sustainability, 2.5–2.8 eV from the temperature dependent Nagoya University, Furo-cho, Chikusa-ku 464-8601, annealing experiments, which is well consistent Nagoya, Japan with the theoretical results from first-principles National Institute for Materials Science, 1-1, Namiki, 305- calculations. 0044 Tsukuba, Japan Institute of Post-LED Photonics, Tokushima University, 2- Characterization of inhomogeneous Ni/GaN 1 Minami-Josanjima, 770-8506 Tokushima, Japan Schottky diode with a modified log-normal Department of Electrical Engineering and Computer distribution of barrier heights Science, Nagoya University, Furo-cho, Chikusa-ku 464- The Bradley Department of Electrical and Computer 8603, Nagoya, Japan Engineering, Virginia Polytechnic Institute and State Institute of High Pressure Physics, Polish Academy of University, Blacksburg, VA 24060, United States of Sciences, Sokolowska 29/37, Warsaw 01-142, Poland America Akasaki Research Center, Nagoya University, Furo-cho, Department of Material Science and Engineering, Virginia Chikusa-ku 464-8603, Nagoya, Japan Polytechnic Institute and State University, Blacksburg, VA Venture Business Laboratory, Nagoya University, Furo- 24060, United States of America cho, Chikusa-ku 464-8603, Nagoya, Japan

Semiconductor Science and Technology AIP Advances https://doi.org/10.1088/1361-6641/ab3071 https://doi.org/10.1063/1.5114866

The current versus voltage (I-V) characteristics of a In this study, V-shaped dislocations in a GaN Ni/GaN Schottky diode are measured from 50 to epitaxial layer on a free-standing GaN substrate 400 K and the temperature dependence of the were observed. Our investigation further revealed

GaNEX | III-N Technology Newsletter No. 81 | 42 that the V-shaped dislocations were newly Influence of photoexcited carriers on generated at the interface in the epilayer rather compositional measurements by APT: AlGaN alloy than propagated from the GaN substrate. V-shaped case study dislocations consist of two straight parts. The Fundamental Technology Research and Development straight parts of the V-shaped dislocations were Division 2, Sony Corporation, Atsugi, Kanagawa 243- separated from each other in the m-direction and 0014, Japan tilted toward the step-flow direction of the GaN National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan epitaxial layer. The V-shaped dislocations are continuous single dislocations having a Burgers Japanese Journal of Applied Physics vector component of 1a and an intrinsic stacking https://doi.org/10.7567/1347-4065/ab3864 fault between their straight parts. We investigated laser-assisted field evaporation Pendeo-epitaxy of GaN on SOI nano-pillars: phenomena of Al x Ga1−x N alloys with various Al freestanding and relaxed GaN platelets on silicon site fractions x (0.05, 0.10, 0.15, 0.20, and 0.25) with a reduced dislocation density using an ultraviolet (UV, 343 nm) femtosecond laser Université Grenoble Alpes, CEA-LETI, 17 Rue Des Martyrs, to clarify the role of the photoexcitation process. 38054 Grenoble, France While the measured Al site fractions largely deviate Université Côte d’Azur, CRHEA-CNRS, Rue Bernard from the corresponding nominal fractions when the Gregory, 06560 Valbonne, France Université Grenoble Alpes, CNRS LTM, 17 Rue Des band gap energy is higher than the photon energy, Martyrs, 38054 Grenoble, France these deviations of the measured Al site fractions decreased for band gap energies smaller than the Journal of Crystal Growth photon energy. We also observed notable https://doi.org/10.1016/j.jcrysgro.2019.125235 improvements in the artifacts on 3D image reconstruction and the measured Al compositions Nanopendeo-epitaxy of gallium nitride (GaN) is using a deep UV (257 nm) laser, which offers a considered in this study as a way of producing photon energy that is higher than the band gap and freestanding GaN with reduced strain and threading the electron affinity. These tendencies indicate that dislocation density (TDD) for optoelectronic both the surface electric field and the applications. The novelty of this work lies in the use photoexcitation process significantly influence the of silicon on insulator (SOI) substrates patterned field evaporation processes. into nano-pillars down to the buried oxide (BOX). We actually want to benefit from the creeping Enhancement-mode n-GaN gate p-channel properties of SiO2 at the growth temperature of heterostructure field effect transistors based on GaN for strain relaxation and grain-boundary GaN/AlGaN 2D hole gas dislocations reduction. In this paper, we report on School of Nano Technology and Nano Bionics, University the fabrication of 40×40 µm2 and 300×300 µm2 of Science and Technology of China, Hefei 230026, freestanding GaN platelets, up to 10 µm-thick, People's Republic of China spontaneously separated from the initial pillars. Nanofabrication Facility of the Suzhou Institute of Nano- Structural and optical characterizations show that Tech and Nano-Bionics, CAS, Suzhou 215123, People's the platelets are crack-free and almost fully relaxed, Republic of China Institute of Microelectronics, Peking University, Beijing with a TDD of ∼ 4×108/cm2. We underline the 100871, People's Republic of China different benefits of this approach, but most Suzhou Powerhouse Electronics Co., Ltd., Suzhou importantly, we believe that it will be the founding- 215123, People's Republic of China brick for transferable GaN-based devices. Applied Physics Letters https://doi.org/10.1063/1.5119985

In this letter, E-mode n-GaN gate heterostructure field effect transistors (HFETs) utilizing polarization GaNEX | III-N Technology Newsletter No. 81 | 43 induced 2D hole gas (2DHG) have been proposed. It Effects of forward gate bias stressing on the is found that the introduction of the n-GaN cap leakage current of AlGaN/GaN high electron between the GaN channel layer and the gate metal mobility transistors can effectively deplete the 2DHG in the gate region, Low Energy Electronic Systems, Singapore-MIT Alliance resulting in E-mode operation. The simulation for Research and Technology, 138602, Singapore results indicate that by adjusting the GaN channel School of Material Science and Engineering, Nanyang thickness and n-GaN cap doping concentration, Technological University, 639798, Singapore Department of Material Science and Engineering, threshold voltage of the n-GaN gate p-channel Massachusetts Institute of Technology, Cambridge, MA HFETs can be more than |−1.5| V without 02139, USA sacrificing the ON-state current and the ON/OFF ratio, which is enabled to overcome the trade-off Microelectronics Reliability observed from conventional p-channel devices. https://doi.org/10.1016/j.microrel.2019.113432

Modeling the Impact of the High-Field Region on Reliability of AlGaN/GaN-on-Si high electron the C−V Characteristics in GaN HEMTs mobility transistors (HEMTs) under forward gate School of Engineering, Macquarie University, Sydney, bias was studied. During stressing, devices were NSW 2109, Australia observed to degrade through an increase in the Fraunhofer Institute for Applied Solid State Physics, gate leakage current. The degradation was 79108 Freiburg im Breisgau, Germany correlated with a decrease in the Schottky barrier

height. Using photon emission microscopy (PEM), IEEE Transactions on Electron Devices https://doi.org/10.1109/TED.2019.2939585 transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS), the In this article, we illustrate the impact of the high physical cause of the degradation was identified as electric field region and the effects of this has on localized carbon residue at the AlGaN/Ni gate the capacitance-voltage characteristics of a GaN interface. HEMT device. Such effects arise due to a significant spike in the electric field near the drain-side edge of Leakage current and rectification behavior of Au / the gate electrode. The presence of the high electric TiO2 / GaN junctions with TiO2 interlayer oxygen field has a direct impact on the intrinsic deposition pressure capacitances of the device. We present a physics- Departmnet of Physics, Kyungpook National University, based compact model for the gate charge and Daegu, South Korea Departmnet of Electrical Engineering, Kyungpook intrinsic capacitances, which captures these effects. National University, Daegu, South Korea TCAD simulations are performed to analyze the underlying principles of such phenomena while Current Applied Physics providing validation for the proposed model. The https://doi.org/10.1016/j.cap.2019.09.018 advanced SPICE model for GaN HEMTs (ASM-GaN- HEMT) is adopted and modified to include the Au/TiO2/GaN junctions with a TiO2 interlayer were effects of the high electric field region. The deposited at various oxygen pressures from 5 mTorr simulation results are in excellent agreement to the to 80 mTorr, and their surface, microstructural, and TCAD and the measured data. The model is electrical properties were investigated. Compared compared to simulations that neglect such effects with a single 5 μm-Si-doped GaN film on an (0001) in order to illustrate the importance of capturing Al2O3 substrate, the 0.2 μm-Si-doped GaN film with the impact of high-field region on the intrinsic an undoped GaN buffer layer demonstrated device capacitances. improved properties for the application to metal/semiconductor junctions. Atomic force microscope and tunneling electron microscope measurements suggested that the TiO2 interlayer deposited at room temperature exhibited a

GaNEX | III-N Technology Newsletter No. 81 | 44 distinctive change above the oxygen deposition concentration and ionization energy were pressure of 40 mTorr. In contrast to the small separately estimated to be (2.6 ± 0.8) × 1018 cm−3 rectification ratio of 101-102 for Au/GaN junctions, and 212 ± 5 meV, respectively. By comparing the the Au/TiO2/GaN junctions with the TiO2 Mg concentrations obtained from secondary ion interlayers displayed a large rectification ratio of mass spectrometry, the acceptor activation ratio 106-107 when the oxygen pressure during the (acceptor concentration/Mg concentration) of the deposition of TiO2 interlayer was maintained at 40 UHPA samples exceeded 70%. These results suggest mTorr. These results suggest that the leakage that the UHPA process as a postimplantation current and the rectification behavior in a annealing technique is promising for the fabrication metal/oxide/semiconductor junction can be of GaN-based power devices with selective area effectively controlled using the oxygen deposition doping. pressure for an oxide interlayer. The interface of epitaxial nanographene on GaN by Highly effective activation of Mg-implanted p-type PECVD GaN by ultra-high-pressure annealing School of Optoelectronic Science and Engineering & IMaSS, Nagoya University, Aichi 464-8601, Japan Collaborative Innovation Center of Suzhou Nano Science Department of Electronics, Graduate School of and Technology, Soochow University, Suzhou 215006, Engineering, Nagoya University, Aichi 464-8601, Japan China ISET, ULVAC, Inc., Chigasaki, Kanagawa 253-8543, Japan Key Lab of Advanced Optical Manufacturing Technologies Toyota Central R&D Labs., Inc., Nagakute, Aichi 480- of Jiangsu Province & Key Lab of Modern Optical 1192, Japan Technologies of Education Ministry of China, Soochow Institute of High Pressure Physics, Polish Academy of University, Suzhou 215006, China Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO), Chinese Academy of Sciences (CAS), Suzhou Applied Physics Letters 215123, P. R. China https://doi.org/10.1063/1.5116866 Suzhou Nanowin Science and Technology Co, Ltd, Suzhou 215123, P. R. China A high activation ratio of acceptors to Mg ions Beijing National Laboratory for Condensed Matter implanted into a homoepitaxial GaN layer was Physics and Institute of Physics, Chinese Academy of achieved through an ultra-high-pressure annealing Sciences, Beijing 100190, P. R. China Collaborative Innovation Center of Quantum Matter, (UHPA) process. Capless annealing under a nitrogen Beijing 100190, P. R. China pressure of 1 GPa in a temperature range of 1573–

1753 K activated acceptors without thermally AIP Advances decomposing the GaN layer. Conventional rapid https://doi.org/10.1063/1.5111443 thermal annealing leads to a serious decomposition at 1573 K, even with an AlN protective cap. The It is believed that directly synthesized graphene on sample annealed at 1673 K under UHPA exhibited semiconductor and other non-catalytic substrates is very intense cathodoluminescence in near-band a promising route to enable facile graphene edge and donor-acceptor-pair band emissions. The integration into commercial electronic and intensities were over one order of magnitude optoelectronic devices. Here, the plasma enhanced higher than those of the sample treated by chemical vapor deposition (PECVD) method has conventional annealing. A Hall-effect measurement been used to synthesize nanographene directly on was obtained in the temperature range of 275– gallium nitride (GaN) at a low temperature (550°C). 500 K for the UHPA sample. The obtained hole The epitaxial nanographene equipped optical concentration and mobility at 300 K were transmittance and conductivity comparable to 3.6 × 1016 cm−3 and 24.1 cm2 V−1 s−1, reduced graphene oxide or chemical exfoliated respectively. The mobility value was close to that of graphene. The Raman spectroscopy and atomic an epitaxial p-type GaN with the same doping force microscopy (AFM) of the samples before and concentration. An Arrhenius plot of hole after growth have been compared. Besides, the concentrations showed that the acceptor GaNEX | III-N Technology Newsletter No. 81 | 45 interface between nanographene and GaN has insulator–semiconductor (MIS) diodes. An been investigated by X-ray photoelectron excessively long duration of oxidation led to the spectroscopy (XPS). This research will be meaningful deterioration of the stoichiometry of the InAlN for directly integrating graphene with GaN-based surface and plasma oxide, resulting in a high- optoelectronic and electronic devices. density of interface states in the completed MIS diodes. Meanwhile, the surface-localized oxygen A polarization-induced 2D hole gas in undoped deficiency in the plasma oxide layer was observed gallium nitride quantum wells by XPS. The intensity ratio of the oxygen-deficient School of Electrical and Computer Engineering, Cornell component to the fully oxidized component in the University, Ithaca, NY 14853, USA O 1s spectrum decreased with increasing oxidation School of Applied and Engineering Physics, Cornell duration. Consequently, there was an optimum University, Ithaca, NY 14853, USA oxidation duration. The interface state density was Department of Materials Science and Engineering, reduced by almost one order in the case of plasma Cornell University, Ithaca, NY 14853, USA oxidation for an appropriate duration compared Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, NY 14853, USA with the case of the direct deposition of SiO2 onto InAlN. Science https://doi.org/10.1126/science.aau8623 Effect of temperature gradient on AlN crystal growth by PVT method A high-conductivity two-dimensional (2D) hole gas, State Key Lab of Crystal Materials, Shandong University, analogous to the ubiquitous 2D electron gas, is Jinan, 250100, P. R. China desirable in nitride semiconductors for wide- Energy Research Institute, Qilu University of bandgap p-channel transistors. We report the Technology (Shandong Academy of Sciences), Jinan observation of a polarization-induced high-density 250014, P. R. China

2D hole gas in epitaxially grown gallium nitride on Cryst. Growth Des. aluminium nitride and show that such hole gases https://doi.org/10.1021/acs.cgd.9b01085 can form without acceptor dopants. The measured high 2D hole gas densities of about 5 × 1013 per In this study, the effect of different temperature square centimeters remain unchanged down to field distributions on the growth of AlN crystal via cryogenic temperatures and allow some of the spontaneous nucleation by PVT method was lowest p-type sheet resistances among all wide- investigated through simulation and experiment. bandgap semiconductors. The observed results The axial temperature gradient increased from provide a probe for studying the valence band 6.71K/cm to 10.85 K/cm, while the radial structure and transport properties of wide-bandgap temperature gradient increased to 4.6 K/cm at first nitride interfaces. and then decreased with the rising of the crucible position. Combining with the growth dynamics Control of plasma-CVD SiO2/InAlN interface by theory, we found that the axial temperature N2O plasma oxidation gradient was the main factor affecting the growth Research Center for Integrated Quantum Electronics, rate of AlN crystal, and the radial temperature Hokkaido University, Sapporo 060-0813, Japan gradient was the driving force for expanding the

Japanese Journal of Applied Physics diameter of AlN crystal. Temperature field https://doi.org/10.7567/1347-4065/ab3c49 simulation and growth dynamics analysis provided a theoretical guide for the growth experiments of AlN Control of the plasma-CVD SiO2/InAlN interface by crystal. When the crucible relative position was N2O plasma oxidation of the InAlN surface was 16%, the radial temperature gradient reached the studied. The interface was characterized by both X- maximum of 4.6 K/cm, and the size of the ray photoelectron spectroscopy (XPS) and spontaneous nucleation grown AlN crystal was the capacitance–voltage measurement of metal– largest. A 2 inch AlN boule was obtained under this

GaNEX | III-N Technology Newsletter No. 81 | 46 temperature field after several runs, and a 5×6 mm, field distribution, it is derived with Bayes’ rule. For 600 μm thick AlN crystal wafer was obtained by the average electric field strength, it is revealed to slicing and polishing. Compared to the initial be quite strong, i.e., in an order of 104 V/cm in GaN spontaneous nucleation, the single crystal size was with a fairly low dopant density. On the basis of the enlarged from ～600 μm to 6 mm. The HRXRD, Franz–Keldysh mechanism, influence of the dopant- Raman and EBSD results showed that the grown induced electric fields on the band-edge absorption AlN crystals had high structure quality and low coefficient of GaN is then investigated. Without any stress. Our study provides an important reference adjustable parameters, absorption coefficients of for growing high quality, large-size AlN crystal. GaN are computed and in good agreement with the available experimental values. Defect energy levels in carbon implanted n-type homoepitaxial GaN ABB Corporate Research, Segelhofstrasse 1K, 5405 Magnetotransport property of graded AlGaN/GaN Baden-Dättwil, Switzerland heterostructure Tianjin Key Laboratory of Low Dimensional Materials Journal of Applied Physics Physics and Preparing Technology, Department of https://doi.org/10.1063/1.5109237 Physics, Tianjin University, Tianjin, 300072, China State Key Laboratory of Infrared Physics, Shanghai While carbon doping is known to increase the Institute of Technical Physics, Chinese Academy of resistivity of GaN, highly resistive layers for device Sciences, Shanghai, 200083, China isolation can also be obtained by ion implantation. School of Material Science and Engineering, Hebei In this study, we report on the electrical University of Technology, Tianjin, 300130, China characterization of C-implanted n-type College of Physical Science and Technology, Guangxi University, Nanning, 530004, China homoepitaxial GaN. Our investigation, carried out by capacitance-voltage measurements and deep Superlattices and Microstructures level/minority carrier transient spectroscopy, https://doi.org/10.1016/j.spmi.2019.106262 revealed the presence of nine majority carrier traps in the 0.2–1.3 eV energy range, below the This paper reports magnetotransport property of a conduction band edge, and of four minority carrier graded AlGaN/GaN heterostructure. When traps, in the 0.1–1.4 eV energy range, above the temperature (T) is higher than 10 K, resistivity as a valence band edge. The net-donor compensation function of T exhibits a metallic conduction mechanism and the behavior of defect centers are behavior, from which the Debye temperature of studied as a function of the annealing temperature 1074.4 K is extracted. At low Ts, clear Shubnikov-de- in the 100–1000 ∘C range. While the former is Haas (SdH) oscillations in magnetoresistance (MR) explained in terms of dynamic annealing, the latter curve are observed when magnetic field is larger is discussed in the light of the present experimental than 2 T. The observed SdH oscillations originate results and those found in the literature. from the two-dimensional electrons. From fast Fourier transform power spectrums of the SdH Dopant-Induced Electric Fields and Their Influence oscillations, it is found that there are five occupied on the Band-Edge Absorption of GaN subbands, in agreement with the results obtained Department of Physics, and Shenzhen Institute of from the energy band calculation. In the Research and Innovation (HKU-SIRI), The University of Hong Kong, Pokfulam Road, Hong Kong, China intermediate field range of MR curve, a parabolic negative MR is observed, which can be attributed to ACS Omega the two-dimensional electron-electron interaction https://doi.org/10.1021/acsomega.9b01394 effect.

Dopant-induced local electric fields and their influence on the band-edge absorption of GaN are theoretically examined. For dopant-induced electric

GaNEX | III-N Technology Newsletter No. 81 | 47

Electronic properties and oxygen chemisorption at above 3.0 mol dm−3 is attributed to common-ion AlxGa1-xN surfaces effects. Profilometric etch rates were lower than Academy of Scientific and Innovative Research, CSIR-NPL coulometric and amperometric etch rates reflecting Campus, Dr. K.S. Krishnan Marg, New Delhi-110012, India formation of a surface film. SEM and profilometry Advanced Materials & Devices Division, CSIR-National demonstrated that thick surface films are formed at Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi, lower concentrations. Etch rates increased linearly 110012, India with light intensity indicating a carrier-limited

etching regime: a quantum efficiency of 57.6% was Materials Chemistry and Physics https://doi.org/10.1016/j.matchemphys.2019.122106 obtained. At light intensities greater than ∼35 mW cm−2 the etch rates showed evidence of saturation. The presented work investigates the impact of AFM and SEM images of the etched GaN surfaces aluminium composition on chemical state and showed a distinctive ridge-trench structure with a electronic properties of AlxGa1-xN/GaN (x = 0.45, hexagonal appearance. Photoluminescence spectra 0.62 and 0.75) heterostructures using of the etched GaN show a significant increase in the photoemission spectroscopy. Extensive core level defect-related yellow luminescence peak suggesting and valence band analysis revealed significant correlation to the formation of the ridge structures, variation in chemical coordination, electron affinity which may represent dislocations terminating at the and valence band hybridization with aluminium surface. composition. The variation in aluminium molar fraction lead to perturbed energetics and changed Sacrificial layer for laser lift-off process for flexible- the oxygen chemisorption mechanism at the display production surface (i.e. electron-counting & oxide- Yerevan State University, Department of Inorganic Chemistry, 1 A.Manukyan st, Yerevan, 0025, Armenia stoichiometry). AlxGa1-xN surfaces with lower Department of Nano-Optical Engineering, Korea aluminium composition also pursued higher density Polytechnic University, Siheung, 429-793, Republic of of donor like surface states. However, the electron Korea affinity of the films decreased from 2.6 to 2.1 eV Department of Renewable Energy, Jungwon University, with increment in aluminium composition and Goesan-gun, Chungbuk, 367-805, Republic of Korea material bandgap. Department of Metallurgical & Materials Engineering, Inha Technical College, Incheon, 402-752, Republic of A Study of the Photoelectrochemical Etching of n- Korea GaN in H3PO4 and KOH Electrolytes Department of Physics, Bernal Institute, University of Vacuum Limerick, Ireland https://doi.org/10.1016/j.vacuum.2019.108968

ECS J. Solid State Sci. Technol. In this study, we developed a new sacrificial layer https://doi.org/10.1149/2.0082001JSS (SL) for laser transfer process. Metallic substrate i.e. invar foil was temporarily docked to a glass We investigated the photoelectrochemical etching substrate using glass powder. To ensure successful of n-GaN in H3PO4 and KOH as a function of delamination, the SL was pre-deposited between electrolyte concentration, potential and light metal foil and glass substrate. For the first time, the intensity. Etch rates measured by stylus SLs were amorphous gallium nitride and non- profilometry were compared with coulometric and stoichiometric gallium oxide which were amperometric values. In both electrolytes, etch implemented for laser lift off (LLO) processes of rates increased with concentration, reaching a metal foil. Bonding of metal foil to glass sheet was maximum at 3.0 mol dm−3 and decreasing at higher performed using heat treatment while debonding concentrations. The increase in etch rate with was achieved by LLO method. The laser wavelength concentration of either H3PO4 or KOH reflects the was 355 nm which was the best fit for full amphoteric nature of gallium and the decrease absorption from SL layers. Transmission electron

GaNEX | III-N Technology Newsletter No. 81 | 48 microscopy, element mapping, and energy and shielding parameters of the SQUID were 0.67 dispersive X-ray spectroscopy analyses were and 0.15, respectively. The SQUIDs in the array performed for investigating elements’ migration were coherently modulated by injecting current in a and bonding-debonding mechanism. common flux control line, which resulted in a modulation voltage of 3.54 mV with consistent Dopant-Induced Electric Fields and Their Influence periodicity and a flux-to-voltage transfer coefficient on the Band-Edge Absorption of GaN of 23 mV/Ф 0 . Using a flux locked loop circuit, the Department of Physics, and Shenzhen Institute of fabricated NbN SQUID array exhibited excellent Research and Innovation (HKU-SIRI), The University of performance with a low white flux noise of 1.4 μΦ 0 Hong Kong, Pokfulam Road, Hong Kong, China /√Hz, which included the preamplifier noise.

ACS Omega Terrestrial neutron-induced single events in GaN https://doi.org/10.1021/acsomega.9b01394 Aix-Marseille University, CNRS, IM2NP (UMR 7334),

Faculté des Sciences, Service 142, Avenue Escadrille Dopant-induced local electric fields and their Normandie Niémen, F-13397 Marseille Cedex 20, France influence on the band-edge absorption of GaN are theoretically examined. For dopant-induced electric Microelectronics Reliability field distribution, it is derived with Bayes’ rule. For https://doi.org/10.1016/j.microrel.2019.06.049 the average electric field strength, it is revealed to be quite strong, i.e., in an order of 104 V/cm in GaN We study the physical mechanisms of single event with a fairly low dopant density. On the basis of the production in GaN wide-bandgap semiconductor Franz–Keldysh mechanism, influence of the dopant- subjected to atmospheric high-energy (>1 MeV) induced electric fields on the band-edge absorption neutron irradiation. The interactions of incident coefficient of GaN is then investigated. Without any neutrons with the target material are investigated adjustable parameters, absorption coefficients of with Geant4 and the transport of the deposited GaN are computed and in good agreement with the charge simulated using our random-walk drift- available experimental values. diffusion (RWDD) modeling approach in a generic reversely biased bulk junction. Fabrication and Characteristics of All-NbN SQUID Series Array Effect of fully strained AlN nucleation layer on the Chinese Academy of Sciences, Shanghai Institute of AlN/SiC interface and subsequent GaN growth on Microsystem and Information Technology, Shanghai, 4H–SiC by MOVPE China Department of Chemistry, Jamia Millia Islamia, ,New Center for Excellence in Superconducting Electronics, Delhi, India Chinese Academy of Sciences, Shanghai Institute of Solid State Physics Laboratory (SSPL), DRDO, New Delhi, Microsystem and Information Technology, Shanghai, India China Journal of Materials Science: Materials in Electronics IEEE Transactions on Applied Superconductivity https://doi.org/10.1007/s10854-019-02247-3 https://doi.org/10.1109/TASC.2019.2938582 AlN nucleation layers (NL) with different thickness In this article, an all-NbN superconducting quantum were grown on 4H-SiC substrates using MOVPE. The interference device (SQUID) array was developed growth evolution of the AlN layer on SiC was for future applications by taking advantage of the investigated. The effect of fully strained AlN higher critical temperature of a NbN film compared nucleation layer (NL) on the AlN/SiC interface and with Nb. The NbN SQUID array was composed of on the subsequent GaN growth was also 100 SQUIDs with equal loop areas connected in investigated. The thickness of the NL was varied series. The array was fabricated on a single-crystal between 10 nm and 100 nm in order to study the MgO (100) substrate using 3- μ m-diameter surface morphology and strain of AlN NL layer. The NbN/AlN/NbN Josephson junctions. The hysteresis

GaNEX | III-N Technology Newsletter No. 81 | 49 interface quality between AlN and SiC was a lower density and a higher magnetization than the characterized using HRXRD. It was observed that main volume of the ɛ−Fe2O3 film. The density and 100 nm NL was partially relaxed whereas 40 nm AlN magnetic moment depth profiles derived from NL was fully strained with improved SiC/AlN fitting the reflectometry data are in a good interface. GaN layer grown with fully strained NL agreement with the presence of the magnetically showed improved surface morphology and lower degraded γ−Fe2O3 transition layer between MgO screw dislocation density. 2DEG properties of and ɛ−Fe2O3. The natural occurrence of the AlGaN/GaN HEMT structures grown on fully interface between magnetoelectric ɛ- and spin strained and partially relaxed NL were found to be caloritronic γ-iron oxide phases can enable further almost similar. opportunities to design novel all-oxide-on- semiconductor devices. Stabilization of ε−Fe2O3 epitaxial layer on MgO(111)/GaN via an intermediate γ-phase The Endocyclic Carbon Substituent of Guanidinate Laboratory for Neutron Scattering and Imaging (LNS), and Amidinate Precursors Controlling ALD of InN Paul Scherrer Institute (PSI), CH-5232 Villigen, Films Switzerland Department of Physics, Chemistry and Biology, Linköping Ioffe Institute, 194021 Saint-Petersburg, Russia University, SE-581 83 Linköping, Sweden Institut Laue-Langevin, 71 Avenue des Martyrs, 38042 Grenoble, France J. Phys. Chem. C https://doi.org/10.1021/acs.jpcc.9b07005 PHYSICAL REVIEW MATERIALS https://doi.org/10.1103/PhysRevMaterials.3.094401 Indium nitride (InN) is an interesting material for future high frequency electronics, due to its high In the present study we have demonstrated electron mobility. The problematic deposition of epitaxial stabilization of the metastable InN films currently prevents full exploration of InN magnetically hard ɛ−Fe2O3 phase on top of a thin based electronics. We present studies of atomic MgO(111) buffer layer grown onto the GaN (0001) layer deposition (ALD) of InN using In precursors surface. The primary purpose to introduce a 4-nm- with bidentate ligands forming In–N bonds; thick buffer layer of MgO in between Fe2O3 and tris(N,N-dimethyl-N’,N’’- GaN was to stop thermal migration of Ga into the diisoproprylguanidinato)indium(III), tris(N,N’- iron oxide layer. Though such migration and diisopropylamidinato)indium(III) and tris(N,N’- successive formation of the orthorhombic GaFeO3 diisopropylformamidinato)indium(III). These was supposed earlier to be a potential trigger of the compounds form a series were the size of the nucleation of the isostructural ɛ−Fe2O3, the present substituent in the endocyclic position decreases work demonstrates that the growth of single from –NMe2, to –Me and to –H, respectively. We crystalline uniform films of epsilon ferrite by pulsed show that when the size of the substituent laser deposition is possible even on the MgO decreases, InN films with higher crystalline- and capped GaN. The structural properties of the 60- optical quality, lower roughness and an In/N ratio nm-thick Fe2O3 layer on MgO/GaN were probed by closer to unity is achieved. From quantum chemical electron and x-ray diffraction, both suggesting that calculations we show that the smaller substituents the growth of ɛ−Fe2O3 is preceded by formation of lead to less steric repulsion and weaker bonds a thin layer of γ−Fe2O3. The presence of the between the ligand and In centre. We propose that magnetically hard epsilon ferrite was independently these effects render a more favoured surface confirmed by temperature dependent chemistry for the nitidisation step in the ALD cycle magnetometry measurements. The depth-resolved which explains the improved film properties. x-ray and polarized neutron reflectometry reveal that the 10 nm iron oxide layer at the interface has

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PRESS RELEASE Technical and economic information selected by Knowmade

ELECTRONICS

Qorvo GaN technology to upgrade US Army radar system SemiconductorToday Qorvo Inc of Greensboro, NC, USA (which provides core technologies and RF solutions for mobile, infrastructure and defense applications) says that one of its gallium nitride (GaN) power amplifiers has been selected by Lockheed Martin to provide GaN modules for production of the US Army’s Q-53 radar system. The insertion of GaN technology into this multi-mission mobile radar is expected to provide superior efficiency, power density, reliability and life-cycle cost over the gallium arsenide (GaAs) amplifiers currently used in the system.

The S-band monolithic microwave ntegrated circuit (MMIC) high-power amplifier (HPA) is built on Qorvo’s gallium nitride on silicon carbide (GaN-on-SiC) technology. The GaN HPA delivers more than twice the saturated output power and a 15-point improvement in power-added efficiency (PAE) over the GaAs predecessor.

These capabilities support the required functions of the phased-array Q-53 radar, such as long-range counterfire acquisition. The amplifier’s compact size and exceptional performance supports a wide range of challenging operating conditions. GaN-on-SiC technology has the added benefit of increasing system reliability and reducing life-cycle ownership costs.

“GaN-based amplifiers are providing RF system engineers with the flexibility to achieve significantly higher power and efficiency than GaAs while using fewer parts,” notes James Klein, Qorvo’s president of Infrastructure and Defense products. “The Q-53 radar system exemplifies just how closely Qorvo works with its defense customers to bring commercial technology to military applications that operate across the spectrum with the highest levels of reliability and functionality,” he adds.

Lockheed Martin has used an open GaN foundry model leveraging relationships with commercial suppliers, like Qorvo, that utilize the power of the expansive telecoms market. This process takes advantage of the commercial industry’s investment in GaN, enables competition and ultimately reduces costs.

FBH presenting III-V electronics portfolio at European Microwave Week SemiconductorToday In a joint booth (B2200) with ‘Research Fab Microelectronics Germany’ (FMD) at European Microwave Week (EuMW 2019) in Porte de Versailles Paris, France (1-3 October), Berlin-based Ferdinand-Braun-Institut, Leibniz- Institut für Höchstfrequenztechnik (FBH) is presenting its portfolio of III-V-based electronics (components for the digitization of mobile communications, for industrial and biomedical systems, and for space applications), including a selection of new developments in power amplifiers, circuits and heterointegrated chips.

In addition to its components for 5G, space communications, and terahertz systems for imaging techniques, FBH is showing a live demonstrator for pulsed laser sources. Using a particularly fast-switching gallium nitride (GaN)- based driver, the pulse length and intensity can be flexibly adjusted between 200ps and 20ns. The system can be flexibly equipped with laser diodes of various wavelengths (630-1180nm). For example, in light detection &

GaNEX | III-N Technology Newsletter No. 81 | 51 ranging (LiDAR) systems, wavelength-stabilized laser diodes emitting at 905nm with 100W peak output power and pulse widths of 3-10ns are used.

Components for 5G and for satellite communications and sensors

Information and communication technologies account for 5% of global energy consumption – in the telecoms sector alone, demand is rising by 10% each year. The projected 5G systems will use higher frequencies, enabling larger signal bandwidth. FBH is presenting two approaches to improve their energy efficiency: a fully digital transmitter architecture and supply voltage modulation for linear amplifiers.

For future mobile communications, FBH is developing digital power amplifiers with efficient amplifier chips based on its 0.25µm GaN-HEMT process. The institute has hence realized the first fully digital transmitter chain that transmits broadband signals with maximum efficiency and linearity (47% at >52dB ACLR). The compact digital transmitter is particularly suitable for multi-antenna systems (massive MIMO) where it can be mounted on the rear side of the antenna.

As a second approach, systems are realized whose supply voltage is modulated and which are suitable for 5G and satellite communications. Their specialty is the efficient amplification of signals with high modulation bandwidths. Together with the European Space Agency (ESA), FBH has developed a novel envelope tracking (ET) demonstrator for communication in space at 1.62GHz. The amplifier has a peak output power of more than 90W with a modulation bandwidth of 40MHz. With an 8.6 PAPR (peak-to-average power ratio) signal, overall efficiency reaches 40%.

Concepts using modulated supply voltage are now also transferred to millimeter-wave amplifiers, which is an interesting option for 5G base stations. FBH has developed a corresponding module consisting of two identical MMICs connected in series. Each consists of a single-stage amplifier with an integrated two-stage voltage switch (class G). The module operates in the 20-26GHz range with 14dB gain and more than 2W/mm at 20V supply voltage.

For satellite sensors, FBH is also developing a modular MIMO radar at 85-95GHz based on FBH’s indium phosphide (InP) transfer-substrate double heterojunction bipolar transistor (DHBT) process. The imaging radar will be used to locate and track objects in the vicinity of satellites. For this purpose, a complete chipset was developed and integrated into a module. The chipset uses novel monolithic microwave integrated circuits (MMICs) with a high output power of >15dBm, a low noise figure (NF) <9dB and frequency converters down to the baseband.

Terahertz detectors and arrays for imaging systems

The terahertz (THz) range offers good spatial resolution and can penetrate most non-metallic materials. It is therefore suitable for a wide range of industrial and safety-relevant applications. However, there are still no imaging systems available with sufficiently high sensitivity and readout speed in this frequency range. Among other things, sensitive, fast and cost-effective THz detectors are missing that offer the potential to be used in THz cameras.

FBH has developed such detectors, which can easily be assembled into arrays. The III-V-based THz detectors offer superior values for the equivalent noise power NEP <25pW/sqrt(Hz) with a highest sensitivity of >100mA/W at 500GHz. These values are said to exceed the best THz detectors available in CMOS technology. The plan is now to develop THz cameras with similar values and an image refresh rate of more than 500 frames per second.

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Transphorm adds first PQFN88-packaged GaN FETs to Gen III product line SemiconductorToday Transphorm Inc of Goleta, near Santa Barbara, CA, USA — which designs and manufactures JEDEC- and AEC- Q101-qualified high-voltage (HV) gallium nitride (GaN) field-effect transistors (FETs) for high-voltage (HV) power conversion applications — has announced its first Gen III PQFN88 transistors. The new 650V devices are available in two versions, the TP65H070LSG (source tab) and TP65H070LDG (drain tab), and offer an on- resistance of 72mΩ.

Transphorm claims that its Gen III devices (launched in June 2018) came onto the market as the highest-quality, highest-reliability [Q+R] GaN FETs available. They pair a custom-designed low-voltage MOSFET with the GaN FET to offer: • quieter switching; • higher performance at increased current levels with minimal external circuitry; • increased noise immunity (threshold voltage at 4V); and • increased gate robustness (at +/-20V). The Gen III drain and source PQFN88 packages include wider pins for increased board-level reliability (BLR), which increases the reliability of multi-layer printed circuit board (PCB) designs. Offering the drain and source tab configurations also accommodates both high- and low-side switch locations. This provides increased radiated immunity as the large pad is soldered to the non-switching node. Further, adding PQFN88 devices to the existing list of Gen III TO-XXX FETs gives engineers an opportunity to explore GaN-driven surface-mount applications using Transphorm’s latest technology.

“Our focus continues to be on increasing GaN FET reliability while delivering higher power density,” says Philip Zuk, VP of technical marketing worldwide & North America sales. “As market interest in high-voltage GaN technology continues to grow, we also aim to arm our customers with device options that fit each potential application. To that end, the introduction of the 72mΩ source and drain PQFN88 devices allows us to meet all three objectives as we fill out our current product family.”

The adoption rate of high-voltage GaN power electronics is on the rise, notes Transphorm, which has announced several customers with diverse end products [e.g. server and industrial power supplies, gaming PC supplies, portable solar generators, etc].

The 650V TP65H070LSG and TP65H070LDG (72mΩ) FETs are currently available for $7.47 in 1000-unit quantities. Supporting design resources include: • TP65H070L series datasheet; • TP65H070L series spice model; • 1.2 kW half-bridge buck or boost evaluation kit [TDHBG1200DC100-KIT]; • TP65H070L half-bridge daughter card [TDHB-65H070-DC]; and • ‘Recommended External Circuitry for Transphorm GaN FETs’ app note.

New start-up Diamond Microwave Ltd signs licensing agreement for GaN-based SSPAs SemiconductorToday Diamond Microwave Ltd (DML) of Shipley, UK, a technology startup specializing in compact gallium nitride (GaN)-based solid-state power amplifiers (SSPAs) for application such as radar, communications and electronic warfare (EW), has signed a licensing deal with Diamond Microwave Devices Ltd (DMD) to continue to grow the commercial base for DMD’s compact high-power microwave amplifiers, and to take DMD’s proprietary technology into new markets.

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“We are delighted to have formed this commercial partnership with DMD, and we look forward to focusing on the exploitation of the DMD amplifier technology in the global marketplace for high-power microwave systems,” says Dr Richard Lang, a director and shareholder of DML (formerly the CEO of DMD).

EPC launches third edition of GaN textbook with power conversion applications focus SemiconductorToday Efficient Power Conversion Corp (EPC) of El Segundo, CA, USA – which makes enhancement-mode gallium nitride on silicon (eGaN) power field-effect transistors (FETs) for power management applications – has announced publication of the third edition of ‘GaN Transistors for Efficient Power Conversion’, a textbook written by power conversion industry experts and published by John Wiley and Sons (available at amazon.com).

The textbook is designed to provide power system design engineering students, as well as practicing engineers, basic technical and application-focused information on how to design more efficient power conversion systems using gallium nitride-based transistors.

The third edition has been substantially expanded to keep students and practicing power conversion engineers ahead of the learning curve in GaN technology advancements and emerging applications. The book serves as a practical guide for understanding basic GaN transistor construction, characteristics, and a wide range of applications. Included are: • discussions on the fundamental physics of these power semiconductors; • practical guidance on layout and other circuit design considerations; • application examples employing GaN including LiDAR for autonomous vehicles, DC-DC power conversion, RF envelope tracking used in 5G communication networks, wireless power, class-D audio and high-radiation environments.

The book offers “a comprehensive view, from device physics, characteristics and modeling to device and circuit layout considerations and gate drive design, with design considerations for both hard switching and soft switching,” comments Dr Fred C. Lee, director of the Center for Power Electronics Systems at Virginia Tech. “Additionally, it further illustrates the utilization of GaN in a wide range of emerging applications.”

All four authors have doctorates in scientific disciplines and are widely recognized published authors. They are pioneers in the emerging GaN transistor technology, with Dr Alex Lidow concentrating on transistor process design and Drs Michael DeRooij, Johan Strydom, David Reusch and John Glaser focusing on power transistor applications.

WIN offers sample kits for NP15-00 GaN-on-SiC 0.15μm-gate technology SemiconductorToday WIN Semiconductors Corp of Taoyuan City, Taiwan – the largest pure-play compound semiconductor wafer foundry – has developed sample kits for its gallium nitride (GaN)-based 0.15μm-gate technology. The NP15-00 millimeter-wave (mmWave) compound semiconductor technology is suitable for transmit power amplifiers used in 5G mmWave radio access networks, satellite communications and radar systems.

Supporting full monolithic microwave integrated circuits (MMICs), the NP15-00 platform allows customers to develop compact, linear or saturated high-power amplifiers up to 35GHz. In the 29GHz band, NP15-00 technology offers saturated output power of 3W/mm with 13dB linear gain and greater than 50% efficiency without harmonic tuning.

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For mmWave active arrays, the higher transmit power and efficiency from the NP15-00 platform affords designers greater flexibility to optimize antenna count, power amplifier size and total array power. Depending on the application, mmWave radio access network (RAN) infrastructure will leverage access points of various sizes, shapes and power levels, and a broad trade-space is crucial to optimize the performance and economics of mmWave active antenna systems, says WIN.

The NP15-00 gallium nitride technology employs a source-coupled field plate for improved breakdown voltage, and operates at a drain bias of 20V. This technology is fabricated on 100mm silicon carbide substrates with through-wafer vias for low inductance grounding.

WIN is celebrating its 20th anniversary and showcasing its compound semiconductor RF and mm-Wave solutions in booth 1220 at European Microwave Week (EuMW 2019) in Paris, France (29 September – 4 October).

Power Integrations delivers millionth GaN-based InnoSwitch3 IC SemiconductorToday Power Integrations of San Jose, CA, USA, which provides high-voltage integrated circuits for energy-efficient power conversion, has delivered its one-millionth InnoSwitch3 switcher IC featuring its PowiGaN gallium nitride technology.

CEO Balu Balakrishnan presented the millionth GaN-based IC to Steven Yang, CEO of Anker Innovations in an event at the latter’s Shenzhen headquarters. Anker is a manufacturer of chargers and adapters, supplying retailers worldwide with powerful, compact USB PD adapters and a range of chargers and adapters for laptops, smart mobile devices, set-top boxes, displays, appliances, networking gear and gaming products.

InnoSwitch3 offline CV/CC flyback switcher ICs with PowiGaN technology are up to 95% efficient across the load range. The very low switching and conduction losses of PowiGaN’s primary switch allows the delivery of as much as 100W from a space-saving InSOP 24D surface-mount package in enclosed adapter applications without requiring a heat-sink. Quasi-resonant InnoSwitch3-CP, InnoSwitch3-EP and InnoSwitch3-Pro ICs combine the primary power switch, primary and secondary control with a safety isolated high-speed link (FluxLink) in between, as well as the secondary SR driver and feedback circuits in a single surface-mount package. Power Integrations says that the switching performance of PowiGaN technology results in substantially higher efficiency, enabling very compact adapter designs.

“Anker is a world leader in compact charger design, and was the first high-volume customer for InnoSwitch3 products with PowiGaN,” says Balakrishnan, who thanks Yang for his “critical contribution to the first successful mass-market deployment of high-voltage GaN technology.”

“By using PowiGaN-based InnoSwitch3 ICs we are able to offer USB PD chargers that are compact, lightweight and capable of delivering high power output,” comments Yang.

BAE Systems completes Phase 1 of transitioning USAF’s short-gate GaN technology to Advanced Microwave Products Center SemiconductorToday BAE Systems has completed a Phase 1 effort to transition short-gate gallium nitride (GaN) technology developed by the US Air Force to its Advanced Microwave Products (AMP) Center in Nashua, NH, USA. It has also been selected by the Air Force Research Laboratory (AFRL) for Phase 2 of the program.

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The GaN technology provides high efficiency and broad-frequency bandwidth capabilities in a compact form that can be integrated into a variety of systems to enable next-generation radar, electronic warfare (EW) and communications.

As part of Phase 2, the BAE Systems FAST Labs R&D team and the AMP Center will collaborate to further develop and advance the readiness of the technology. Specifically, the project will scale the 140nm GaN monolithic microwave integrated circuit (MMIC) technology to 6-inch wafers and increase its manufacturing level of maturity as part of the validation process, which will include optimizing performance, ensuring process stability, and maximizing wafer-to-wafer uniformity and wafer yields. Custom MMIC design company ENGIN-IC will support the design activities, including process design kit (PDK) validation. This technology will transition to a foundry service product, available through BAE Systems’ open foundry service, at the end of Phase 2, where the technology can be leveraged more broadly across different government initiatives.

“Our foundry is a trusted partner to the defense community because it is dedicated to the design, creation and implementation of vital technologies such as short-gate GaN,” says Chris Rappa, product line director for Radio Frequency, Electronic Warfare, and Advanced Electronics at BAE Systems FAST Labs. “GaN technology fills a unique need for the Department of Defense for low-cost, high-performance amplifier technology, and Phase 2 of this effort brings us one step closer to successfully manufacturing and bringing AFRL’s technology to market,” he adds.

BAE Systems is researching and developing microelectronic technologies, including GaN, in its 70,000ft2 Microelectronics Center (MEC) in Nashua, NH. The MEC has been an accredited DoD Category 1A Trusted Supplier since 2008, and fabricates integrated circuits in production quantities for critical DoD programs.

OPTOELECTRONICS

BluGlass-Bridgelux JDA to evaluate RPCVD and tunnel junction technologies for cascade LEDs in general lighting market SemiconductorToday BluGlass Ltd of Silverwater, Australia – which was spun off from the III-nitride department of Macquarie University in 2005 – has entered into a joint development agreement (JDA) with Bridgelux Inc of Fremont, CA, USA (a vertically integrated manufacturer of solid-state light sources for lighting applications) to build on BluGlass’ remote-plasma chemical vapor deposition (RPCVD) tunnel-junction technology in order to develop cascade LEDs, establish a path for mainstream applications in the growing general lighting market.

For over 15 years, Bridgelux has designed and produced LED lighting solutions for the general lighting market that are said to be high performing, energy efficient, cost effective and easy to integrate. Its focus on technology development has yielded proprietary innovations in LED design and manufacturing processes that enable its products to accelerate the mass adoption of LED lighting.

BluGlass’ unique RPCVD technology is a low-temperature, ammonia-free process that is claimed to offer performance advantages for electronics manufacturers including higher-performing, lower-cost devices. The firm recently demonstrated patented ‘active as grown’ RPCVD tunnel junctions for LED wafers. It is reckoned that these tunnel junctions could solve the industry challenge of efficiency droop, by combining multiple LEDs in a single vertical LED stack, generating greater light output for less power.

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The joint development program aims to integrate BluGlass and Bridgelux’s technologies in high-performance commercial LED applications, and to ultimately drive commercial adoption of RPCVD-enabled cascade LEDs for general lighting through the future provision of RPCVD equipment and process licensing. The terms of the JDA are non-exclusive and will provide foundry revenue to BluGlass for its development work.

“Bridgelux is a leader in solid-state lighting innovation and is always working on developing new technologies for the LED lighting industry,” says Bridgelux’s CEO Tim Lester. “We look forward to exploring the potential of RPCVD with BluGlass,” he adds.

“We are delighted to have Bridgelux as a development partner to help deliver the competitive advantages of RPCVD tunnel junctions into this important high-growth market,” says BluGlass’ CEO & managing director Giles Bourne. “Bridgelux is an innovative leader producing premium lighting to high-end markets around the globe. This commercial partnership marks an exciting milestone for BluGlass.”

Monolithic alternating current indium gallium nitride light-emitting chips SemiconductorToday Pennsylvania State University in the USA claims the first monolithic integration of high-breakdown Schottky barrier diodes (SBDs) and indium gallium nitride (InGaN) light-emitting diodes (LEDs) to give single chips operated by alternating current (AC) [Jie Liu et al, IEEE Transactions On Electron Devices, published online 8 August 2019]. The 3W device therefore combines the high voltage and light-emitting capabilities of the III- nitride platform. The SBDs are used to convert the AC power source to direct current (DC).

Key to the development was the use of a cyclic etching process involving ‘dry’ plasma and ‘wet’ solution steps to reduce surface defect energy levels interfering with the performance of the SBDs. The researchers comment: “We believe that the approach of fixing the reactive ion etching-induced defects of III-nitrides with cyclic mixed- etching could potentially be extended to the development in micro-LED display devices where the pixelated LEDs suffer from low efficiency due to the presence of high-density surface states on the pixel sidewalls.”

The epitaxial material used for the AC-LEDs (Figure 1) was from a commercial off-the-shelf product supplied by “a major LED wafer manufacturer”.

Inductively coupled plasma (ICP) etch to a depth of 4.5μm created isolation mesas for the SBD and LED devices. Further ICP etch exposed the n-GaN Ohmic contact regions of the LEDs at a depth of 1.2μm.

The mixed wet/dry etch process was used to remove the LED layers from the SBD mesa, leaving the unintentionally doped GaN surface. Three cycles of the mixed etch was used to give a low density of the surface defects on the unintentionally doped GaN layer of the SBD. The cycle consisted of reactive ion etch using a chlorine-based ICP, followed by boiling potassium hydorxide (KOH) solution. The unetched regions were protected using a patterned nickel hard mask. After the mixed etch, an anneal step raised the temperature to 750°C for 2 minutes in a nitrogen atmosphere.

The p-GaN contact of the LED was indium tin oxide (ITO). The n-GaN contacts of the LED and SBD consisted of titanium/aluminium/titanium/gold (Ti/Al/Ti/Au). These electron-beam evaporated contacts were designed to be Ohmic. The nickel/gold (Ni/Au) Schottky contact on the unintentionally doped GaN was thermally evaporated.

The device surfaces were passivated with plasma-enhanced chemical vapor deposition (PECVD) 500nm-thick silicon dioxide. Contact was made through the passivation using via holes. The metal interconnects for the micro-LED arrays and Schottky diode-based bridge rectifier monolithic circuit consisted of Ti/Al/Ti/Au.

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Figure 1: (a) Circuit configuration of AC-LED. (b) Schematic of monolithically integrated LED and SBD. (c) Microphotograph of fabricated AC-LED die.

The cyclic etch process gave SBDs with a reverse breakdown voltage of more than 120V, compared with ~27V for devices produced using a conventional etch. The forward voltage of the 120V SBDs was ~2.6V at 20mA injection. The reverse leakage was less than 10μA at 100V bias.

The researchers comment: “The measurement result clearly reveals that the cyclic mixed-etching recipe developed in this work restores the ICP-etched GaN surface to device quality and suppresses the reverse leakage of the Schottky junction of Ni/GaN effectively.” They further suggest that the KOH treatment removes nitrogen vacancies in the GaN, reducing the surface defect donor density.

The micro-LED pixels measured 390μmx325μm. The turn-on voltage for 0.1mA current was 2.56V. The external quantum efficiency was 41.5% at 3.8V and 25mA injection.

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Single-chip AC-LED circuits were produced with lateral dimensions of 2.12mmx2mm. The monolithic circuit integrated 28 cascaded micro-LEDs and a bridge rectifier circuit of 8 SBDs. The bridge circuit used 2 SBDs in each branch to handle higher voltages. The SBD had 3 interdigitated Schottky contact fingers that were 20μm wide and spaced at 20μm intervals. The bridge circuit accounted for 11% of the device area. Putting 2 SBDs in each branch enabled rectifying voltages of up 240V, which should be sufficient to enable DC conversion of single- phase US line voltages. The AC-DC conversion efficiency of the bridge circuit was estimated to be 89% from various tests.

Figure 2: Pictures of packaged AC-LED devices mounted on circuit board and prototype AC-LED lamp with remote phosphor.

The chips were attached to copper heat-sinks with thermally conductive adhesive. Gold wiring connected the devices to the external leads of the packaging. The die was encapsulated in high-refractive-index silicone with a transparent hemispheric plastic cover. The device was then mounted on a printed circuit board and placed in a lamp fixture with a remote phosphor plate with the aim of producing ~5000K white light.

The AC-LED assembly was subjected to 110V root-mean-square (rms) 60Hz power. The measured rms current was 20.6mA with around 82% power factor. The luminous efficacy was 89lm/W. The researchers estimate the heat load of the SBDs at 120VAC was 0.28W, or 9.2% of the overall LED power. The researchers comment: “This power loss is comparable with that (~10%) of a reactive 10%) of a reactive ballast used in compact fluorescent lamps as reported in the general electric technical bulletin. While the incandescent lamps operate in the black- body radiation mode and do not have any drivers as well as the relevant power losses, the luminous efficacy of incandescent lamps is less than 1/5th of the AC-LED lamps reported herein.”

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Improving white light-emitting diode luminous efficiency and color rendering SemiconductorToday Researchers based in China have combined phosphors, quantum dots and metal nanoparticles to create blue-to- white light converters for indium gallium nitride (InGaN) light-emitting diodes (LEDs) with simultaneously improved luminous efficiency and color rendering [Rongqiao Wan et al, Optics Letters, vol44, p4155, 201]. Often improved color rendering comes at the cost of reduced luminous efficiency.

The approach adopted by Central South University, Semiconductor Lighting Technology Research and Development Center, and University of Chinese Academy of Sciences, enables a broader spectrum of light over the visible range, filling in the red end of the spectrum, compared with the lost-cost white LEDs using yellow phosphors that are presently in mass production.

The researchers combined green-emitting and red-emitting phosphors with silver (Ag) and gold (Au) nanoparticles (NPs). The broadband green emitter consisted of cerium-doped lutetium aluminium garnet (LuAG:Ce, Al5Lu3O12). Core/shell cadmium selenide/zinc sulfide (CdSe/ZnS) quantum dots (QDs) in toluene solvent provided a narrowband blue-to-red converter. The Ag NPs, on average, were 15nm diameter, and the Au NPs 70nm diameter. The NPs were dispersed in toluene.

The materials were mixed into silicone gel, and the mixture was placed in vacuum for 90 minutes to remove the toluene. The gel was then dropped onto 10milx23mil 451nm blue LED chips in a lead frame. The blue electroluminescence of the LEDs had a full-width at half maximum (FWHM) of 17nm. Thermal curing at 130°C lasted 15 minutes. All the samples contained the green phosphor and red QDs, but some also contained silver (Ag-WLEDs) or silver and gold (AgAu-WLEDs) NPs to give white LEDs. The samples without NPs were designated wo-WLEDs.

Figure 1: Schematic mechanisms and energy transfer paths for (a) wo-WLEDs; (b) Ag-WLEDs; and (c) AgAu- WLEDs.

The blue-to-white conversion layer was designed to take advantage of a variety of physical processes (Figure 1). The green (544nm wavelength under photoluminescence, 106nm FWHM) and red (613nm, 30nm FWHM) phosphors/QDs operated through Stokes processes of absorption of blue photons and emission of the longer- wavelength, lower-energy green and red light. Since green light has higher photon energy than red, some green- to-red conversion might also be expected. The use of QDs was also expected to add non-radiative energy transfer (NRET) channels between the green and red emitters.

The metal NPs were also hoped to provide NRET enhancement. The Ag NPs also absorbed the main blue light (454nm absorption peak) from the LED active region through localized surface plasmon resonance (LSPR). The team comments: “Due to the resonant light scattering effect, the absorption cross section of LuAG:Ce and

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CdSe/ZnS QDs for blue light increases, thus enhancing color conversion efficiency.” Plasmons are oscillations of electron density.

The Au NPs were designed to have localized surface plasmon resonance with the green emissions (531nm peak). The researchers also suggest that the resonance may provide an environment that gives Purcell-effect enhancement of spontaneous emission of the phosphor and QDs.

The researchers first investigated the improvements achievable with varied concentrations of Ag NPs (Table 1). The peak color rendering index (CRI) of 93.6 was achieved with 5 parts per million (ppm) NPs, by weight, and 4A/cm2 current injection. Higher luminous efficiency (LE) of 87 lumens per watt (lm/W) was found with 3ppm NPs at 4A/cm2. The 3ppm Ag-WLEDs also demonstrated the lowest correlated color temperature (CCT) of 5100K at 4A/cm2. A low CCT indicates higher red and green content in the ‘white’ light, which is associated with ‘warmer’ illumination compared with regular white light.

Table 1: CRI, CCT and LE of Ag-WLEDs with varied NP concentrations.

The Ag-WLEDs were further enhanced with Au NPs (Table 2). The Ag NP concentration was fixed at 3ppm. The incorporation of 1ppm Au NPs enabled an increase in luminous efficiency to 92lm/W at 4A/cm2, while the CRI and CCT were 93.2 and 5070K, respectively. Increasing the injection current to 120A/cm2enhanced the CRI to 94.5 (Figure 2). With 1.5ppm Au NPs the luminous efficiency increased to 92.5lm/W at 4A/cm2, but at the cost of reduced 86 CRI.

Table 2: CRI, CCT and LE of AgAu-LED with varied Au NP concentrations and constant 3ppm Ag NPs.

The team expects further enhancements from “package and energy transfer structure optimization” to reduce energy losses.

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Figure 2: (a) Electroluminescence spectra of Ag-WLEDs and AgAu-WLEDs with varied concentration of Au NPs and constant 3ppm Ag concentration under 20mA (16A∕cm2) injection current. (b) CIE-1931 chromaticity coordinates of AgAu-WLED, (c) CRI, (d) CCT and (e) LE of Ag-WLEDs and AgAu-WLEDs versus current density.

Plessey produces record 2.5μm-pixel-pitch 4Megapixel GaN-on-Si micro-LED display SemiconductorToday Using its propriety monolithic gallium nitride on silicon (GaN-on-Si) technology, UK-based Plessey, which develops embedded micro-LED technology for augmented-reality and mixed-reality (AR/MR) display applications, has produced a record 2.5μm-pixel-pitch micro-LED display.

The ultra-fine, ultra-high-resolution 2000x2000-pixel display uses micro-LEDs, a technology that is playing a critical role in the development of next-generation wearables, AR/VR hardware and heads-up displays (HUDs). They require about 20% of the power of typical LCOS (liquid crystal on silicon) or DLP (digital light processing) displays and can achieve five times brighter images than organic light-emitting diodes (OLEDs), allowing comfortable outdoor viewing.

“Pixel pitch is key to the physical size of large field displays and to the resolution of the viewed image,” notes Clive Beech, senior director, business development. “These are key attributes in AR systems. The 2k2k display scale can be realised in a compact physical form factor and the 2.5μm pixel pitch achieves image features with smooth borders and fine detail,” he adds. “An example of Plessey’s latest scalable pixel architecture, these micro-LED display products will enable many new innovations and exciting applications in both augmented reality (AR) and mixed reality (MR) smart glasses.”

The low thermal resistance of the silicon substrates allows highly efficient heat extraction, resulting in lower junction temperatures with high reliability, says Plessey. The GaN-on-Si technology also allows what is said to be high energy efficiency, high resolution and unsurpassed contrast. With its similarity to large-scale silicon IC processing, the technology can be scaled to progressively larger wafers, improving cost, uniformity and yield and taking advantage of the latest advances in silicon wafer processing tools of the volume IC industry.

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Plessey says that other recent milestones in its monolithic micro-LED emissive display program include the development in March of native green GaN-on-Si LEDs that naturally emit blue light. May’s SID Display Week 2019 event saw the world’s first monolithic GaN-on-Si micro-LED emissive display with an 8μm pitch bonded to a backplane for a full active matrix.

Plessey notes that its ongoing micro-LED display development roadmap includes the production of a full RGB display all on one wafer by 2020’s Consumer Electronics Show (CES).

High-power LED market growing at 5.3% CAGR to $17,581.5m in 2024 SemiconductorToday The high-power light-emitting diode (LED) market was $12,647.2m in 2018 and will rise at a compound annual growth rate (CAGR) of 5.3% from 2019 to $17,581.5m in 2024, according to a report by P&S Intelligence. The major factors stimulating growth include rising adoption of energy-efficient lighting solutions and increasing government support for the adoption of LED lights globally.

Based on wattage, the high-power LED market is classified into 1–2.9W, 3–4.9W, 5–10W and >10W. Among these, the 5–10W category is expected to see the fastest growth due to the rising deployment of 5–10W high- power LEDs in general lighting applications, such as outdoor lighting and entertainment lighting.

By application, the high-power LED market is segmented into automotive, general lighting, backlighting, signs & signals, and others (including camera flash lighting, infrared emitters and ultraviolet LEDs). Of these, the automotive category is projected to register a CAGR of 5.4% due to increasing demand for high-power LEDs in both exterior and interior applications, such as fog lights, position lights, headlights, ambient lighting and dashboard lights. In addition, demand for high-power LEDs in backlighting application (including gaming, channel letter lighting and portable appliances) has risen significantly and is projected to grow steadily.

Geographically, the Asia-Pacific (APAC) region is expected to account for a substantial share of the high power LED market, due mainly to the growing adoption of high-power LEDs in general lighting, mainly in China and India. Also, several smart-city development projects are in the pipeline in these countries, which are expected to generate huge demand for high-power LED lights. For example, China introduced a national development project in 2012 to build smart cities with modern technology. Further, the Chinese government aims to nurture 100 new smart cities to lead their urban planning and development by 2020.

Rising adoption of energy-efficient products, along with increasing government focus toward energy saving, is fueling the demand for energy-efficient lighting sources, predominantly high-power LEDs, which is likely to

GaNEX | III-N Technology Newsletter No. 81 | 63 bolster the growth of the high-power LED market. High-power LEDs are particularly advantageous in general lighting and automotive applications as they work efficiently for long operating hours at low maintenance cost. Due to these advantages, local authorities of countries, such as the USA, India, China, and Australia, have commenced projects to replace their conventional lighting lamps used in outdoor lighting with LEDs. For example, in 2014, according to the US Department of Energy, the city of Los Angeles had completed a citywide street lighting replacement program and installed over 215,000 LED streetlights (saving about $9m in annual energy costs).

Furthermore, in 2016, the Institute of Public Works Engineering Australasia (IPWEA) and the Australian government together showcased a strategic roadmap to promote LED lights to increase energy efficiency under the Street Lighting and Smart Controls Programme. Hence, an increasing number of government initiatives to reduce energy consumptions is expected to bolster high-power LED market growth in the future.

The high-power LED market is highly competitive and fragmented, with the presence of a large number of global and regional players. Some of the key players include Cree Inc, Osram Licht AG, Nichia Corp, Samsung Electronics Co Ltd, Seoul Semiconductor Co Ltd, Everlight Electronics Co Ltd, Lumileds Holding B.V., MLS Co Ltd, LG Innotek Co Ltd, Broadcom Inc, and Epistar Corp. These companies are adopting product launches, as a key strategy, to maintain their stronghold in the market, says the report.

For example, in May 2018, Samsung Electronics introduced LED components for horticultural lighting. Its new horticulture LED lineup features a newly developed red LED package, in addition to key existing Samsung white LED package and module families to include horticultural lighting specifications.

Most recently, in May 2019, Lumileds introduced two new additions to its LUXEON chip-on-board (COB) LED family. The LUXEON COB Core Range and the LUXEON COB with CrispWhite Technology can deliver a minimum of color rendering index (CRI) of 95 for applications such as indoor lighting and retail lighting.

Evatec wins repeat order for thin-film production equipment from micro-LED firm PlayNitride SemiconductorToday Evatec AG of Trübbach, Switzerland (which makes thin-film production equipment for advanced packaging, power device, MEMS, optoelectronics, wireless communication and photonics applications) has secured a follow-up order for the delivery of multiple fully automated thin-film production tools to Taiwan-based micro-LED specialist PlayNitride Inc, enabling the ramp up of its gallium nitride (GaN)-based micro-LED production.

With their advantages of high pixel density, high contrast ratio and brightness (all at low power consumption), micro-LED displays offer new opportunities for next- generation consumer devices and large premium displays.

“With our complete thin-film process portfolio for metals, transparent conductive oxides (TCOs), passivation layers and DBRs, Evatec sputter technology was already well established at the world’s leading LED manufacturers on substrate sizes up to 8 inch,” says Dr Stefan Seifried, head of Evatec’s Optoelectronics business unit. “A first order for our fully automated cassette-to- cassette production tool by leader PlayNitride back in 2017 allowed us to demonstrate the capability of our tool to deliver highly uniform films at even lower particle and defect levels essential for the high-yield production of micro-LED,” he adds. “Playnitride has now shown its confidence in our tool performance by placing follow-up orders to deliver tools carrying out a range of production processes for its GaN-based micro-LEDs. Its great to see micro-LED technology and use developing so quickly.”

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Plessey Launches A MicroLED Direct-Drive Display Platform CompoundSemiconductor Plessey has introduced a microLED Direct-Drive display platform and development kit, based on its proprietary monolithic GaN-on-Silicon technology.

The company says its Direct-Drive displays provide OEM's and product developers with a solution to retrofit current products or develop new concept designs, around a compact, flexible and highly efficient microLED display.

Direct-Drive targets specialised applications that require symbolic content, instead of individually addressed pixelised content. Due to the small form factor of the Direct-Drive display, it can be integrated into smart glasses, and head-mounted displays for navigation, sport & leisure, and optical instruments.

The symbolic content is fully customisable using monochrome or fully colourised segments with pixel capabilities down to 2-micron, allowing for ultra-fine, ultra-high-resolution detail. The display is self-emissive, and it can be driven directly from an external source, requiring no backplane which simplifies the manufacturing process and improves power consumption.

The Direct-Drive development kit is a starter package designed to be a fast, easy and scalable platform allowing developers to explore, evaluate and interact with small-form factor microLED displays.

Samir Mezouari, optical engineering manager at Plessey said: “With a total input power of 250 mW, Plessey's native green segments can emit 2 million nits of brightness. For AR applications, the Direct-Drive displays can achieve a much higher brightness than OLED with a power consumption as low as 50 mW, allowing daytime viewing and a longer battery life.”

The Direct-Drive development kits will be available to order at CES 2020 and are targeted toward keen display technology enthusiasts and system engineers looking for a microLED display solution to enhance their products.

Silver nanoparticle boost to gallium nitride red light-emitting diodes SemiconductorToday Osaka University in Japan has combined silver nanoparticles (Ag NPs) with europium-doped gallium nitride (GaN:Eu) light-emitting diodes to boost red electroluminescence by a factor of two [Jun Tatebayashi et al Appl. Phys. Express, vol12, p095003, 2019]. The output power enhancement is attributed to coupling between local surface plasmon (LSP) free-electron oscillations on the Ag NPs and electron transitions in the Eu ions that produce red photons.

The GaN:Eu LEDs operate through ~620nm-wavelength transitions in the electronic state of the Eu3+ ions, rather than the band-to-band transitions of indium gallium nitride (InGaN) devices, for which ~520nm green wavelengths are a struggle to obtain efficiently.

The research team points out that stable, narrow-wavelength GaN:Eu red LEDs “have recently reached output- powers respectable for commercialization.” They suggest that further performance enhancements could lead to applications such as in micro-LED displays with red, green and blue emitters on a common GaN platform.

The GaN layers were applied using metal-organic vapor phase epitaxy (MOVPE) on sapphire via trimethyl- gallium and ammonia precursors (Figure 1). The GaN:Eu,O co-doped layer used in addition bis(n-propyl- tetramethyl-cyclopentadienyl)europium (EuCppm2) and argon-diluted O2 sources. The n- and p-type silicon and

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Figure 1: Schematic of fabricated LEDs.

The growth sequence was: 530°C GaN buffer, 1.5μm 1200°C undoped GaN, 2.4μm n-GaN contact, 100nm 960°C GaN:Eu,O active layer, and 1050°C p-GaN contact.

Further processing consisted of 10-minute 800°C annealing in nitrogen to activate the p-GaN doping, formation of self-assembled Ag nanoparticles, 150nm indium tin oxide (ITO) sputtered p-contact, and chromium/gold (Cr/Au) metal contact electron-beam deposition.

Inductively coupled plasma etch was used to expose the n-GaN layer for the metal contact deposition. The final devices were 1mmx1mm in lateral dimensions.

The nanoparticle formation consisted of electron-beam deposition of a silver film, followed by annealing at 200°C for 30 minutes in nitrogen.

Photoluminescence (PL) experiments on the epitaxial material with Ag NPs showed a 622.4nm peak at room temperature. The peak shifted to 621.8nm at 10K. The emission was attributed to 5D0–7F2 transitions in the Eu. At 10K, there are also “several” lesser peaks either side of the main one. [I see two (with a broad ~10nm hump on the short-wavelength side) in the image in the paper, but maybe these break up into “several” at higher resolution.] These peaks become less clearly defined at room temperature. The different peaks are attributed to variations in the electromagnetic environment of the Eu3+ ions in the GaN crystal structure.

“This is a result of the existence of defects such as Ga and N vacancies, as well as carbon, oxygen and hydrogen, yielding various ‘Eu incorporation sites’, and also modifies the transition probabilities of each Eu site,” the team explains.

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The intensity of the emissions generally increased with the thickness of the Ag film used to create the NPs – at 20nm the intensity was 3.4x that for the bare material at room temperature (6.65x at 10K). There was a slight intensity dip initially with 5nm Ag, before enhancements set in with thicker Ag films.

The researchers comment: “The observed enhancement of the luminescence intensity is predominantly a result of coupling of the Eu3+ luminescence to the LSP modes of Ag NPs, although a small increase due to reflection at the GaN/Ag NPs interface might be expected after the formation of Ag NPs.”

The PL studies did not show near-band-edge emissions from the GaN material (in the near ultraviolet) or ‘yellow luminescence’ associated with crystal defects. The team writes: “This indicates that electron-hole pairs generated in the GaN host can be efficiently captured to the trap level responsible for energy transfer from the host material to the Eu3+ ion.”

Time-resolved PL analysis at 10K found that the decay time with 20nm Ag NPs was shorter than that for bare material – 204μs, compared with 263μs. The 1.3 increased decay probability was taken as deriving from the coupling between the Eu ions and the LSPs of the Ag NPs. In fact, the decay time was minimized at 194μs with NPs created with 15nm Ag films. The researchers tentatively attribute the increase with 20nm Ag to “the irregular shape and large size variation” of the NPs reducing the coupling with the Eu ions.

The LSP-ion coupling is seen as being rather small, compared with conventional indium gallium nitride (InGaN) quantum well and surface plasmon structures reported in the scientific literature. The researchers suggest that this is due to the much thicker GaN:Eu,O layer, compared with quantum wells – 100nm versus 1-3nm, typically.

Figure 2: (a) Output-power versus injection current of fabricated GaN-Eu-based LEDs with and without Ag NPs. (b) EL spectra of GaN:Eu-based LEDs under 100mA injection current. Inset shows microscopic image of red LEDs.

Electroluminescence performance was assessed for radiation extracted out of the sapphire back-side of the device (Figure 2). The onset of light emission came at around 10mA current injection. The researchers say that optimization of the thickness and doping density of the p-GaN layer is required to reduce current leakage while maintaining coupling efficiency between the LSP and GaN:Eu layers. The light output saturated around 100mA. The device with Ag NPs had 2.1x the output without the particles at 100mA.

While it is tempting to increase the emission by increasing the Eu concentration, this runs the risk of reducing crystal quality and thus the light emission performance

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Mini-LEDs to continue to see higher penetration rates in high-end display markets SemiconductorToday Mini-LED backlight displays all have a significant advantage in brightness, reliability and performance, as well as a chance to grab a slice of the high-end display market, according to the latest ‘Mini-LED and HDR High-End Display Market Report’ by LEDinside (a division of TrendForce). Mini-LED backlights may even extend the lifetime of LCD displays, seeing penetration rates of 20%, 15% and 10% in the IT, TV and tablet application markets, respectively, in 2024.

Comparing the features of organic light-emitting diode (OLED) and mini-LED backlight displays, the local dimming feature of mini-LED backlight displays may rival OLEDs in their ability to contrast colors, notes TrendForce. Mini-LEDs also have more competitive prices compared with TV and monitor product applications, since mini-LED backlight displays exhibit display effects nearly equal to those of OLEDs, but the power consumption is much lower than for OLEDs. So, these products give better value for money.

Epistar develops fast transfer technology to enter mini-LED backlight market

With the rise of mini-LED backlight technology, the original industry chain has changed, says the report. For example, panel manufacturers AUO and Innolux are both collaborating with their respective LED companies to develop mini-LED backlight modules: AUO has joined with Lextar, while Innolux is already working with companies such as AOT and Epileds, developing towards TV, IT and small- and medium-sized automotive product applications and hoping to keep their competitive edge in LCD products. CSOT, BOE and others have got involved in mini-LED backlights and display businesses by leveraging their edge in product technology and equipment CapEx. Chip manufacturer Epistar has worked with subsidiary Yenrich to release mini-LED light source modules to enter the backlight applications of high-end displays.

The key challenges of mini-LED backlight technology are cost, power consumption and die-bonding efficiency. In terms of the challenge of power consumption, as current mounts (and heat along with it), efficiency declines. So far, Epistar has offered two different solutions to help customers meet their goal of reducing power consumption or cost. For power consumption, with the decrease in chip size and drive current, customers can improve full-screen power consumption with enhanced backlight dimming zone control. For cost, Epistar has added an innovative reflector with LED chips to increase the beam angle. So far, Epistar has been able to produce LED chips with special beam angle of 150-170° to reduce both number of LED chips required and system production costs.

In addition, with the reduction of LED chip size and the increase in number, LED die bonding is becoming increasingly difficult. Epistar and subsidiary Yenrich’s self-developed ‘Fast Transfer on X substrate’ can precisely transfer mini- or micro-LED chips in large quantities on a variety of material substrates specified by customers.

TrendForce says that innovations in mini-LED backlight technology may bring advantages in display effect, but the new structure also places a heavier burden in costs, and striking a fine balance between the two has become a problem that suppliers along the whole supply chain must work together to solve. The fastest way to reduce costs would be to combine the strengths of relevant suppliers for backplanes, LED chips and driver ICs and module assembly companies and to develop mini-LED products with better value. Mini-LED chips will play an important role in that process, reckons TrendForce. Chip suppliers turned market leaders and technological vanguards will hold an even greater advantage in the future, the firm concludes.

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CSC collaborates on commercializing Kubos’ cubic GaN technology for green and amber LEDs SemiconductorToday The Compound Semiconductor Centre Ltd (CSC) – a joint venture founded in 2015 between Cardiff University and epiwafer foundry and substrate maker IQE plc of Cardiff, Wales, UK – and Kubos Semiconductors Ltd of Cambridge, UK have signed a memorandum of understanding (MoU) to pursue the commercialization of cubic gallium nitride (GaN) epitaxial technology for high-efficiency LED lighting applications. The agreement aims to accelerate the development of Kubos’ IP on metal-organic chemical vapor deposition (MOCVD) reactors at CSC’s St Mellons facility, via the collaboration of CSC, Kubos, IQE and Cambridge University staff.

Kubos is an early-stage start-up formed in 2017 to develop and commercialize its proprietary cubic GaN intellectual property (IP). The firm has an exclusive license to the technology, which was originally developed in partnership with the Department of Materials at the University of Cambridge and Anvil Semiconductors.

Kubos’ cubic GaN growth technology is reckoned to have the potential to circumvent some of the key limitations in conventional GaN-based LED devices. In particular, the removal of internal electric fields and a narrower bandgap mean that cubic GaN can deliver more efficient green and amber LEDs, overcoming the so-called ‘green gap’ problem. This can facilitate improved displays and also light bulbs that can be varied to mimic the natural changes in daylight through the day.

The CSC facility in St Mellons is co-located with significant volume manufacturing capacity of its JV owners IQE, so the infrastructure provides the advantage of seamless scale up from low-volume R&D and prototyping activities through to process transfer onto Aixtron MOCVD production tools, installed during a £10m capital investment completed at the site in 2017.

“This is a great example of our ability to accelerate new epitaxial technologies to market by supporting an ecosystem where academic researchers work in an industrially relevant environment,” says CSC’s director Dr Wyn Meredith. “It provides a very low-cost model for spinouts and new ventures to leverage the significant capital investment required to commercialize new epitaxial technologies. The cost and risk of commercialization is reduced with the added benefit of working with a wide range of relevant capability and partners in the emerging CSconnected compound semiconductor cluster in South Wales,” he adds.

“CSC is an ideal partner for Kubos as it supports our fabless business model and assists with the tight control of R&D costs,” comments Kubos’ CEO Caroline O’Brien. “As our technology matures it will also mean that we have an established relationship with a partner who can support the move to high-yield, high-volume processes that is required for a commercially viable LED technology.” Once mature, Kubos plans to license the technology to major LED makers.

Reducing power losses in indium gallium nitride laser diodes on silicon SemiconductorToday Researchers in China have reduced the point defects in indium gallium nitride (InGaN) laser diode (LD) material on silicon with the aim of reducing operating voltages and injection current and increasing device efficiency [Jianxun Liu et al, Optics Express, vol. 27, p25943, 2019]. Although silicon-substrate laser diodes benefit from lower cost and raise the prospect of more complex integrated photonics and optoelectronics, efficiencies suffer from the energy-sapping effects of high defect levels.

One problem has been that the lattice mismatch between silicon and gallium nitride (GaN) is about 17%. The thermal expansion mismatch is even greater – around 54%. The lattice/thermal mismatches are now bridged by using various aluminium gallium nitride (AlGaN) alloy layers before the main device layers. Even so, the resulting

GaNEX | III-N Technology Newsletter No. 81 | 69 laser diodes tend to have high threshold currents and voltages, indicating high electrical and optical power losses.

The research team from Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO), University of Science and Technology Beijing, and University of Science and Technology of China, developed a lower-temperature growth process and alternative material structure, in particular layers to reduce threshold currents and voltages by an approximate factor of 2 (72mA/150mA, 4.7V/8.2V).

Figure 1: (a) Schematic diagram of InGaN-based laser diodes grown on Si. (b) Cross-sectional high-angle annular dark-field scanning transmission electron micrograph of InGaN MQW active region.

The laser diode material (Figure 1) was grown on (111) silicon with metal-organic chemical vapor deposition (MOCVD). The n-GaN contact layer was 2.7μm, while the lower cladding was 1.2μm n-Al0.05Ga0.95N. The multiple quantum well (MQW) active layer consisted of three pairs of 2.7nm/12nm 770°C In0.12Ga0.88N/In0.02Ga0.98N. The top p-GaN contact was 30nm thick, and the electron layer (EBL) was Al0.2Ga0.8N.

Two laser diode material samples, A and B, were produced (Table 1). Sample B used lower temperatures in the lower and upper waveguides (WGs), and in the p-type contact layer (CL) superlattices (SLs). Lower temperatures reduced thermal degradation of the MQW region and carbon incorporation from the organic precursors used.

Table 1: Comparison of growth conditions between samples A and B.

Carbon tends to compensate, reducing the effectiveness of the magnesium doping used for the p-type layers needed for hole injection. This is expected to increase series resistance and operation voltage, adding to laser diode power losses. Lower carbon levels are also associated with lower optical absorption.

The researchers comment: “It is noted that the adoption of InGaN/GaN SL WG would cause little effect on the thermal conductivity of the laser diode structure, because there was only a trace amount (1% in average) of indium in such SL WGs (sample B), and the total thickness of the In0.01Ga0.99N layer was only 70nm (40 and 30nm for the lower and upper waveguide, respectively), which was negligibly smaller than that of the AlGaN cladding layers (1.8μm in total) and the n-GaN contact layers (2.7μm).”

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Due to the lower growth temperatures, microscopic inspection of photoluminescence (PL) in sample B showed greater uniformity, compared with sample A. The more even PL suggests less degradation of the delicate MQW region. In addition, sample A suffered from a short decay time of 3.5ns, compared with 6.3ns for B, in time- resolved PL. The researchers suggest that the faster decay is due to non-radiative Shockley-Read-Hall (SRH) recombination through mid-gap defect levels. The team adds that SRH recombination results in reduced internal quantum efficiency (IQE, photons/electron) and increased junction temperatures and threshold currents.

The researchers also attribute some of the improvement in sample B’s IQE to replacement of the waveguide layer with InGaN SLs. The high-temperature GaN material tends to contain vacancies on the gallium ion site. Reducing the number of vacancies reduces optical absorption from strong band-tail effects. The silicon doping of the n-GaN layer also contributes band-tail energy states. “Such absorption will increase the internal optical loss and reduce the IQE, resulting in an increase in junction temperature and threshold current for the laser diodes,” the team writes.

The team fabricated edge-emitting laser diodes with ridges 800μm long and 4μm wide. The cleaved front and rear facets of the laser diodes were coated with titanium dioxide/silicon dioxide (TiO2/SiO2) multilayers to increase reflectivity with low optical loss.

Electroluminescence experiments (Figure 2) demonstrated lasing peaks at 413.4nm and 418nm for samples A and B, respectively. The laser diodes were operated in 400ns pulse mode with 10kHz repetition to avoid self- heating effects. The wavelength difference is attributed tentatively to differences in MQW growth temperatures, which can significantly affect indium incorporation.

Figure 2: (a) EL spectra of sample B above (1.2x) and below (0.8x) threshold current. Inset: corresponding far- field patterns. (b) On-bar light output power-current-voltage (L-I-V) characteristics under pulsed injection for samples A and B.

Sample B showed a reduced threshold voltage of 4.7V, compared with 8.2V for sample A. The threshold current for B was also about half that of A: 72mA (2.25kA/cm2) versus 150mA (4.7kA/cm2). Reduced current and voltage, and hence input power, for a given output mean increased efficiency.

In lifetime tests under pulsed-mode operation, sample B laser diodes showed little degradation in output power after 620 hours, unlike devices based on sample A material.

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Plessey’s micro-LED growth technology combines native blue and green epi on single wafer SemiconductorToday UK-based Plessey, which develops embedded micro-LED technology for augmented-reality and mixed-reality (AR/MR) display applications, has extended the capability of its proprietary gallium nitride on silicon (GaN-on-Si) process to enable native blue and native green emission from the same wafer.

The potential of micro-LEDs is well known but several challenges remain before ramping up to large-scale consumer applications. To form RGB micro-LED displays, typical approaches are to use a pick & place process to transfer discrete R, G and B pixels or to use native-blue LEDs as the light source for subsequent colour conversion to red and green.

Plessey’s latest patented growth approach creates both native-blue and native-green emission layers on the same wafer. The monolithic formation of two colours significantly simplifies display manufacture. Green micro- LEDs have high efficiency with a narrow spectral width resulting in what is said to be an excellent colour gamut when operating alongside the high-performance blue micro-LEDs. The firm’s new approach forms micro-LEDs that exhibit high-current-density operation and long operational lifetime.

The monolithic integration of both the native-blue and green micro-LEDs on the same silicon substrate is the result of a concerted effort aimed at solving several challenges previously considered insurmountable. Among the issues preventing the integration of multiple wavelength diode junctions are, firstly, a magnesium memory effect and diffusion from the p-type cladding of the lower junction into the upper junction.

An additional process challenge to the integration of blue and green micro-LEDs is the precise tuning of the thermal budget during growth of the second junction to prevent indium phase separation in the blue active region. Plessey says it has precisely engineered the thermal budget to maintain high efficiency (IQE), low defectivity and high electrical conductivity required for high-brightness display applications.

A final operation in the formation of GaN micro-LEDs is a post-growth treatment aimed at removing hydrogen atoms that would otherwise compromise the conductivity of p-type layers. The presence of a second junction complicates the removal of hydrogen from the buried device structure, negating the effect of standard post-growth activation treatments.

Plessey says it has overcome all these challenges and created a monolithic blue and green micro-LED fabrication process that integrates these junctions vertically, separated by a sub-micron layer thickness, resulting in very reproducible and stable diode performance well beyond what is typical in the LED industry, it is reckoned.

“Our latest breakthrough has a multiplier effect on our previous successes with high-efficiency monolithic native blue arrays, native green arrays and hybrid bonding to backplane by demonstrating a way to synthesize the best of our know-how into a single die,” says Dr Wei Sin Tan, director of Epitaxy and Advanced Product Development. “This has enormous implications and will open the doors towards new innovations across a wide range of GaNEX | III-N Technology Newsletter No. 81 | 72 display applications. For mobile and large displays, a high-efficiency single RGB tile can now be used for mass- transfer and for micro-displays; this creates a path to the elusive single RGB panel ultra-high-resolution micro- LED AR display,” he adds. “This new process paves the way to commercial, high-performance micro-LED displays, bringing mass adoption of micro-LEDs in displays ever closer to reality.”

Micro-LED technology is continuing to emerge as the most likely successor to today’s smart high-performance display applications, making displays with smaller form factor even brighter and more power efficient than existing display technologies available, says Plessey.

Other recent milestones from Plessey includes the first wafer-level bonded monolithic 3000ppi (pixels per inch) GaN-on-Si micro-LED emissive display hybridized to an active-matrix CMOS backplane, and a high-efficiency native-green technology. Plessey says it is continuing to develop micro-LED display solutions with its roadmap including the production of full RGB micro-LED displays by 2020.

OTHER

kSA Emissometer for MOCVD wafer carrier characterization gains UV PL capabilities SemiconductorToday k-Space Associates Inc of Dexter, MI, USA - which supplies in-situ, ex-situ and in-line metrology tools for the thin-film, semiconductor, photovoltaic (PV), solar, automotive, glass and building materials industries – says that the kSA Emissometer ex-situ metrology tool for metal-organic chamical vapor deposition (MOCVD) carrier characterization now has ultraviolet (UV) photoluminescence (PL) capabilities for even better carrier evaluation. The new UV PL feature allows wafer carrier manufacturers, reactor manufacturers and epi houses to further evaluate their wafer carriers before use and throughout their lifecycle. The system uses a 365nm- wavelength LED focused on the wafer carrier and a filtered photodetector focused on the excitation point. The filter cuts off light for wavelengths shorter than 409nm. This results in the ability to evaluate contamination on the wafer carrier.

The kSA Emissometer is used to determine the quality of the carrier bake after the deposition run, quantitative determination of real surface emissivity for temperature set-point adjustments, and microcrack detection. It also provides statistical analysis of each individual pocket and web for carrier quality evaluation. “This tool gives carrier manufacturers, reactor manufacturers and epi houses a competitive edge because it allows them to quantify their carrier quality, ultimately leading to increased device uniformity and increased yield,” says CEO Darryl Barlett.

Riber enters loss in first-half 2019 despite MBE system revenue more than doubling SemiconductorToday Riber S.A. of Bezons, France – which manufactures molecular beam epitaxy (MBE) systems as well as evaporation sources and effusion cells – has confirmed revenue of €13.9m for first-half 2019, down 17% on first- half 2018’s €16.7m.

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Evaporators revenue has fallen by 90% from €10.4m to €1m, but this is deemed to be temporary following the major investments made in previous years.

Systems revenue has more than doubled, rising by 132% from €3.7m to €8.6m, reflecting the strengthening of Riber’s commercial positions in the industrial sector, with four production systems delivered, compared with just one production system and three research systems in first-half 2018.

Services & Accessories revenue grew by 65% from €2.6m to €4.3m, in line with the strategy to develop this activity.

Gross margin has fallen from 48.8% to 29.5% due to the contraction in revenue as well as a product mix that is currently less favorable. Net loss was €0.4m, compared with income of €2.4m in first-half 2018.

Net cash at end-June 2019 was €2.5m, level with with end-December 2018, while shareholders’ equity has fallen from €19.2m to €17.6m due mainly to the first-half loss and recognition of the distribution of amounts drawn against the issue premium to shareholders for 2018, paid out in July and September 2019.

The order book at end-June has fallen year-on-year by 17% from €34.3m to €28.4m, but this is still high, confirming the positive market environment for the production MBE business. Systems orders were down by just 3% from €22.2m to €21.5m (comprising 13 systems, including six production units). Services & Accessories orders fell by 17% from €8.3m to a still “satisfactory” €6.9m. These order book figures do not include the order received in September from Asia for an MBE 6000 production system.

Riber says that, on the basis of the first-half 2019 results, it can hence confirm its full-year forecast for revenue growth and improved operational profitability compared with 2018. The firm adds that, in a buoyant environment driven by information technology innovations over the coming years, it is moving forward with its development, consolidating its market shares, expanding its portfolio of technologies and clients, and supporting the development of its service activities.

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PATENT APPLICATIONS

More than 300 new patent families (inventions) were published in September 2019.

Other patent applicants 13th Research Institute of China Electronics Technology, Asti Global, Beijing University of Technology, BOE Technology, Denso, Guangzhou Guanglian Electronic Technology, Harbin University of Science & Technology, Hebei University of Technology, IBM, Jiangsu Kailun Building Material, Murata Manufacturing, Nagoya University, Nanchang University, Qingdao Goertek Microelectronics Research Institute, Shanghai Institute of Microsystem & Information Technology Chinese Academy of Sciences, Shenzhen China Star Optoelectronics Semiconductor Display Technology, Shindengen Electric Manufacturing, Soitec, South China University of Technology, Suzhou Changrui Photoelectric, Suzhou Hanhua Semiconductor, Suzhou Institute of Nano Technology & Nano Bionics Chinese Academy of Sciences, Taiwan Semiconductor Manufacturing, Taiyuan University of Technology, University of Electronic Science & Technology of China Zhongshan Institute, Vanguard International Semiconductor, Wuhan China Star Optoelectronics Technology, Wuhan University, Zhejiang University, Zheng An County Ruiyuan Tea Industry, 3M, 41medical, ABB Schweiz, Afton Chemical, Akoustis, Azur Space Solar Power, BAE Systems Information & Electronic Systems Integration, Beibei Stem Cell & Regenerative Medicine Translational Research Institute, Beijing Normal University, Beijing Wanji Technology, Carbonex, Cea - Commissariat à L’energie Atomique & Aux Energies Alternatives, Changxin Storage Technology, Chonbuk National

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University Industry Academy Cooperation Foundation, CIS Forschungsinstitut Fuer Mikrosensorik, CNRS - Centre National De La Recherche Scientifique, Cornell University, Cpe Lyon Formation Continue & Recherche, Dalian Xinguan Technology, Dexerials, Dialog Semiconductor, Dongguan BOSMFC Optoelectronics, Ecole Centrale De Lyon, Ecole Polytechnique Federale De Lausanne (EPFL), Epihouse Optoelectronic, Fan Junge, Federalnoe Gosudarstvennoe Avtonomnoe Obrazovatelnoe Uchrezhdenie Vysshego Obrazovaniya Natsionalnyj Issledovatelskij Tomskij, Fuji Electric, Fujian Lightning Optoelectronic, Fujitsu, Fyzikalni Ustav Av Cr V V I, Globalfoundries, Guangzhou Aibei Biological Technology, Guangzhou Tiandian Technology, Guizhou Province Zheng An County Yiren Tea Industry, Hangzhou Haicun Information Technology, Hangzhou Hertak Technology, Hebei Envoltek Electronics Technology, Hohai University, Hospices Civils De Lyon, Hot Wenchuang, Huawei, Huazhong University of Science & Technology, Hubei Surpass Sun Electric, Hunan Forest Botanical Garden.

Notable new patent applications

Reflector, surface emitting laser, method for manufacturing reflector, and method for manufacturing surface emitting laser Publication Number: US20190273360, JP2019153779 Patent Applicant: RICOH

A reflector includes a low refractive index layer and a high refractive index layer. The low refractive index layer has a first average refractive index and has a laminated structure in which an AlN layer and a GaN layer are alternately laminated. The high refractive index layer has a second average refractive index higher than the first average refractive index and includes an InGaN layer.

GaN material and method of manufacturing semiconductor device Publication Number: US20190273137, JP2019153679, CN110223914 Patent Applicant: SCIOCS, SUMITOMO CHEMICAL

There is provided a new technology for anodic oxidation etching performed to GaN material having arithmetic mean line roughness Ra of 15 nm or less at a measurement length of 100 μm on a bottom surface of a recess when anodic oxidation etching is performed at an etching voltage of 1 V while irradiating the GaN material with UV light to form the recess of 2 μm in depth.

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Production method for group III-nitride crystal Publication Number: JP2019151519, US20190271096, CN110219047 Patent Applicant: OSAKA UNIVERSITY, PANASONIC

A production method for a group III nitride crystal, the production method includes: preparing a plurality of group III nitride pieces as a plurality of seed crystals on a substrate, and growing a group III nitride crystal by bringing a surface of each of the seed crystals into contact with a melt that comprises at least one group III element selected from gallium, aluminum, and indium, and an alkali metal in an atmosphere comprising nitrogen, and thereby reacting the group III element and the nitrogen in the melt, wherein the step of growing a group III nitride crystal includes: growing a plurality of first group III nitride crystals whose cross- sections each have a triangular shape or a trapezoidal shape, from the plurality of seed crystals; and growing second group III nitride crystals each in a gap among the plurality of first group III nitride crystal

Image display device Publication Number: US20190273179, JP2019153783, CN110224000 Patent Applicant: SHARP

An image display device includes a drive circuit substrate, micro LED elements, and a wavelength conversion layer that converts excitation light emitted from the micro LED elements and that emits converted long-wavelength light to a side opposite to the drive circuit substrate, the micro LED elements and the wavelength conversion layer being sequentially stacked on the drive circuit substrate. The micro LED elements include a first multilayer film that reflects the long-wavelength light converted by the wavelength conversion layer.

GaN laminate and method of manufacturing the same Publication Number: JP2019151540, US20190272990, CN110219049 Patent Applicant: SCIOCS, SUMITOMO CHEMICAL

To provide a new GaN laminate obtained by growing a GaN layer on a GaN substrate by HVPE, including: a GaN substrate containing GaN single crystal and having a low index crystal plane as c-plane closest to a main surface; and a GaN layer epitaxially grown on the main surface of the GaN substrate, and having a thickness of 10 nm or more, wherein a surface of the GaN layer has a step- terrace structure in which a step having a height of equal to or more than a plurality of molecular layers of GaN and extending in a predetermined direction and a terrace are alternately arranged.

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Nitride semiconductor device Publication Number: WO2019/181391 Patent Applicant: PANASONIC

A nitride semiconductor device (10) according to the present invention is provided with: a substrate (12); a drift layer (14) having a first conductivity type and a first base layer (16) having a second conductivity type, which are sequentially provided on a first main surface (12a) of the substrate (12); a gate opening (22) which penetrates through the first base layer (16) and reaches the drift layer (14); an electron transit layer (26) which is provided above the first base layer (16) along the inner surface of the gate opening (22); a gate electrode (30) which is provided above the electron transit layer (26) so as to cover the gate opening (22); a source electrode (34) which is connected to the first base layer (16); a drain electrode (36) which is provided on a second main surface (12b) of the substrate (12); and a high resistance layer (24) which is provided between the first base layer (16) and the electron transit layer (26) in the gate opening (22), and which is formed of a nitride semiconductor, while having a higher resistance than the first base layer (16).

LED emissive display device and method for producing such a device Publication Number: WO2019/180362, FR3079350 Patent Applicant: CEA

The invention relates to a display device comprising a first integrated circuit (200) comprising: an assembly of light- emitting diodes (103), each diode comprising a vertical stack of a first semiconductor layer (105) having a first type of conductivity and a second semiconductor layer (109) having a second type of conductivity; and, on the side of a face of the first circuit opposite the first semiconductor layer (105), a connection structure (201) comprising a dielectric layer (203) in which there are a plurality of identical or similar connection pads (205) which are regularly distributed over the entire surface of the first circuit, each diode (103) having a first electrode (111) which is in contact with at least one pad (205) of the connection structure (201), and a second electrode (113) which is in contact with a plurality of pads (205) of the connection structure (201) on the periphery of the plurality of diodes.

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Epitaxial semiconductor/superconductor heterostructures Publication Number: WO2019/173448 Patent Applicant: CORNELL UNIVERSITY, US NAVAL RESEARCH LABORATORY

Solid-state devices including a layer of a superconductor material epitaxially grown on a crystalline high thermal conductivity substrate, the superconductor material being one of TiNx, ZrNx, HfNx, VNx, NbNx, TaNx, MoNx, WNx, or alloys thereof, and one or more layers of a semiconducting or insulating or metallic material epitaxially grown on the layer of superconductor material, the semiconducting or insulating material being one of a Group III N material or alloys thereof or a Group 4b N material or SiC or ScN or alloys thereof.

Semiconductor device Publication Number: WO2019/176722, JP2019161013 Patent Applicant: DENSO

Provided is a semiconductor device comprising: a substrate (1); a channel forming layer (7) which comprises a first GaN semiconductor layer (5) and a second GaN semiconductor layer (6) that constitute a heterojunction structure, in which a recessed part (9) is formed by partially removing the second GaN semiconductor layer(6); a gate structure which is constituted by disposing a gate insulating film (10) and a gate electrode (11) in the recessed part (9); a source electrode (12) and a drain electrode (13) which is disposed on the channel forming layer (7) so as to sandwich the gate structure; and a third GaN semiconductor layer (3) which is disposed between the first GaN semiconductor layer (5) and the substrate (1) and is doped with P-type impurity. In the semiconductor device, a fourth GaN semiconductor layer (4) of N-type is disposed between the third GaN semiconductor layer (3) and the first GaN semiconductor layer (5).

Multi-pixel chip and method for producing a multi-pixel chip Publication Number: WO2019/175168, DE102018105786 Patent Applicant: OSRAM

In one embodiment, the optoelectronic multi-pixel chip (1) comprises a plurality of pixels (3) which can be individually electrically activated to generate and emit light. A first semiconductor region (21) extends continuously across the pixels (3). A second semiconductor region (22) is structured on the pixels (3). An active zone (23) for generating the light is disposed between the first and second semiconductor regions (21, 22). A first contact (41) is provided for making electrical contact with the first semiconductor region (21), and a second contact (42) is provided for making electrical contact with the second semiconductor region (42). The active zone (23) is designed to generate the light only in a direction parallel to an emission side (10) of the multi-pixel chip (1). The first semiconductor region (21) has a mushroom-shaped cross-section per pixel (3).

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LED-transistor composite element Publication Number: WO2019/176326, JP2019161172 Patent Applicant: TOHOKU UNIVERSITY, V-TECHNOLOGY

With a view to driving a plurality of light-emitting elements by an active matrix, the present invention eliminates the need for a TFT substrate and enables arranging of a plurality of light-emitting elements in a low-profile and high-density configuration. This LED- transistor composite element is provided with a lamination part obtained by laminating a plurality of n- type or p-type group-13 nitride-based compound semiconductor layers over a thin-film crystalline layer of a group-13 nitride-based compound on a substrate, wherein: the lamination part is provided with a first lamination section equipped with an n-type semiconductor layer and a p-type semiconductor layer with a light-emitting layer being interposed therebetween, a second lamination section which is laid over the first lamination section and in which n-type and p-type semiconductor layers are stacked alternately, and a third lamination section which is laid over the second lamination section via an intermediate insulation film and in which n-type and p-type semiconductor layers are stacked alternately; and an LED, a first transistor, and a second transistor are constituted by the first lamination section, the second lamination section, and the third lamination section, respectively.

Semiconductor device and method for manufacturing same Publication Number: WO2019/176470, JP2019161029 Patent Applicant: TOYOTA CENTRAL RESEARCH & DEVELOPMENT LABS

This semiconductor device 100a includes a substrate 102 and an n-type layer 104 which is formed on the surface of the substrate 102 and made of a nitride semiconductor (A). In the n-type layer 104, the concentration of donor impurities (exclusive of O) is 1×1015 cm-3 to 1×1020 cm-3, the concentration of C impurities is 1×1016 cm-3 or less, the concentration of O impurities is 1×1016 cm-3 or less, and the concentration of Ca impurities is 1×1016 cm-3 or less, and the total concentration of the C impurities, the O impurities, and the Ca impurities is lower than the concentration of the donor impurities. This semiconductor device 100a can be manufactured by using a halogen-free vapor phase epitaxy (HF-VPE) apparatus.

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