DOCSLIB.ORG

Intrinsic Limits of Electron Mobility in Modulation-Doped Algan/Gan 2D Electron Gas by Phonon Scattering

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Intrinsic Limits of Electron Mobility in Modulation-Doped Algan/Gan 2D Electron Gas by Phonon Scattering JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY, VOL. 12, NO. 4, DECEMBER 2014 415 Intrinsic Limits of Electron Mobility in Modulation-Doped AlGaN/GaN 2D Electron Gas by Phonon Scattering Liang Pang Abstract⎯We theoretically present the intrinsic advantage of modulation-doping technique is that nearly all limits to electron mobility in the modulation-doped the carriers are spatially separated from their donor AlGaN/GaN two-dimensional electron gas (2DEG) due impurities, which strongly suppresses the impurity to effects including acoustic deformation potential (DP) scattering effect. Consequently, the 2DEG carrier mobility scattering, piezoelectric scattering (PE), and polar-optic is further enhanced, making the system a good candidate phonon scattering (POP). We find that DE and PE are for high-frequency devices like the HEMTs. However, the more significant limiting factors at intermediate other scattering effects largely influence the transport temperatures of 40 K to 250 K, while POP becomes properties of the 2DEG carriers. The significance of dominant as room temperature is approached. Detailed different scattering mechanisms under different conditions numerical results are presented for the change of like temperature and electron sheet density, and the electron mobility with respect to temperature and limitations that these mechanisms may have on the device carrier density. We conclude that these three types of performance are crucial from both physical and technical phonon scattering, which are generally determined by points of view[6]. The three phonon scattering types the material properties but not the technical processing, investigated in this paper are acoustic deformation-potential scattering (DP), piezoelectric scattering (PE), and are hard limits to the 2DEG mobility. polar-optical phonon scattering (POP), which are the Index Terms⎯AlGaN/GaN, 2-dimensional electron dominant scattering mechanisms for temperature higher gas, electron mobility, phonon scattering. than 40 K. We study their physical importance, summarize their analytical expressions, and investigate their impacts 1. Introduction on the electron mobility under different temperatures or 2DEG sheet densities. The purpose of this review is to Over the past decade, GaN and related nitrides have facilitate a better physical understanding of these particular been intensively studied for the fabrication of high scattering mechanisms, while emphasizing that it is these temperature, high power, and high frequency electronic three intrinsic material properties that determines the devices, due to the material properties such as high critical fundamental limit of carrier mobility for any given material breakdown field, high saturation electron velocity, good systems. chemical inactivity, and thermal stability. The most prominent example is the high electron mobility transistor (HEMT), in which the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface greatly enhances the electron mobility[1][3]. Because of the large conduction band discontinuity between AlGaN and GaN, and the strong polarization-induced electric field at the interface, the AlGaN/GaN quantum well provides enhanced quantum (a) confinement compared to AlGaAs/GaAs counterpart[4]. Two ways are proposed to dope the structure in order to supply carriers in the 2DEG channel, naming uniform-doping as in Fig. 1 (a) and modulation-doping as in Fig. 1 (b)[5]. The Manuscript received October 2, 2013; revised December 20, 2013. This work was supported in part by the Grainger Center for Electric Machinery and Electromechanics of the University of Illinois. (b) L. Pang is with the Department of Electrical and Computer Engineering, University of Illinois, Urbana 61801, USA. (Corresponding author e-mail: Fig. 1. Conduction band diagram of (a) a uniformly-doped danielangp@ gmail.com). AlGaN/GaN/AlGaN heteostructure and (b) a modulation-doped Digital Object Identifier: 10.3969/j.issn.1674-862X.2014.04.014 AlGaN/GaN/AlGaN heteostructure. 416 JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY, VOL. 12, NO. 4, DECEMBER 2014 2. Scattering Mechanisms the solution to the Boltzman equation will yield (1). It should be noted that the solution to the Boltzman equation * The electron mobility, defined by μn=eτ/m , where e is also yields an integral factor term that depends on the angle the electronic charge, τ is the relaxation time, and m* is the between k and k′. However, this term is not included in our effective electron mass, is a critical transport property. calculations since it can be approximated to unity. Although not the focus of this study, it should be noted that 2.2 Piezoelectric Scattering interface-roughness scattering, as well as alloy disorder and For the temperature range used in this study, the dislocation scattering, which are more process-determined [11] factors, are important scattering mechanisms limiting the relaxation rate for PE is given as 2 mobility. Remote modulation-doping scattering from the ⎡⎤2 1913⎛⎞vIzeh 1 ionized impurities in the AlGaN layer is considered =+⎢⎥⎜⎟lt 14 (6) τ ⎢⎥32 32 ⎜⎟vIπτ kE negligible because of the strong screening applied to the PE⎣⎦⎝⎠tl FD DP 2DEG. Consequently, we concern ourselves here only with 1/2 DP, PE, and POP. where kF=(2πns) is the norm of the Fermi wave vector, 2 1/2 2 1/2 It=[(8ħvtkF/3πkBT) +1] , Il=[(8ħvlkF/3πkBT) +1] , z is the 2.1 Acoustic Deformation-Potential Scattering average distance of the electronic wave function from the The relaxation rate for DP is expressed as[7] AlGaN/GaN interface corresponding to the lowest sub-band * 2 (i.e. the width of the quantum well), h14 is the piezoelectric 1 3mEDB kT constant, and vt is the transverse acoustic phonon velocity. = 23 b (1) τρDP 16 vl = The piezoelectric effect is resulted when an electrical where potential is generated in response to a mechanical stress. 13 ⎛⎞33emn2 * This occurs in GaN due to the lack of inversion symmetry b = ⎜⎟s (2) (i.e. GaN has a non-centrosymmetric crystalline structure) 8= 2εε ⎝⎠0 s such that an elastic strain will result in a polarization of the [12] is a variational parameter, vl is the longitudinal acoustic unit cell . Piezoelectric scattering is the additional * phonon velocity, ED is the deformation potential, m is the coupling between the acoustic phonons and the free carriers effective electron mass, kB is the Boltzmann constant, T is caused by this potential. GaN along with other nitrides have the temperature, ρ is the mass density, h is the Plank relatively large piezoelectric constants among III-V constant, e is the electron charge, ns is the conduction semiconductors, so the piezoelectric scattering must be electron concentration, ε0 is the vacuum permittivity, and εs taken into account. Here we will examine (6) to determine is the relative permittivity. The origin of (1) is briefly the dependence of piezoelectric scattering on temperature discussed here. and electron sheet density. The variational parameter b comes from the Fang- [8] Howard wave function 2.3 Polar-Optical Phonon Scattering [14] 1 For POP, the relaxation rate is expressed as ψ ()zb=− (3 /22 )2 z exp( bz / ) (3) FH 1 2emN2 * ()( TGk ) = B 0 (7) which is used for triangular potential wells and in our case * 2 τ POP ε = fyPOP () appropriately describes the confinement profile of electrons −1 −1 in the 2DEG. Based on the typical acoustic where ε=ε0/(ε∞ −εs ) is the effective dielectric constant, [9] ħω is the polar optic phonon energy, k =(2m*ħω /ħ2)1/2 deformation-potential electron scattering rate in 3D, SIII , POP 0 POP [10] is the electron wave vector corresponding to the phonon the scattering rate for 2D electrons, SII, is given by energy, NB(T)=1/[exp(ħωPOP/kBT)−1] is the phonon 2 SIqSdq= () (4) occupation number described by the Bose-Einstein II∫ z III z distribution, and fPOP=1+(1−exp(−y))/y is a function with a 2 * where q=|k−k′ |, qz is the z-component of q, and I(qz) is dimensionless variable y=πħ ns/m kBT. The value of G(k0) [10] given by is determined from the Fang-Howard wave function as[14] 2 22 I()qziqzdzzz= ψ FH ()exp() . (5) bb()89++ kb 3 k ∫ Gk()= 00. (8) 0 8()bk+ 3 By solving the Boltzman transport equation for low 0 electric fields and using the principle of detailed balance, POP is an important mechanism in GaN and other III-V we can apply SII to a 2D linearized version of the Boltzman compounds because of the opposite ionic charges on the equation. Assuming the equi-partition regime, then the two atoms. A distortion in the crystal lattice will result in a phonon occupation number is Nq, which can be macroscopic field that scatters the electrons. The long- approximated by kBT/ħωq. If we also assume that the range potential results in a scattering rate matrix element acoustic phonon scattering is elastic, then ħωq drops out of that is inversely proportional to |k−k′|. This means that the the Dirac delta function inside SII. With these assumptions, scattering prefers small angles and we do not have the PANG: Intrinsic Limits of Electron Mobility in Modulation-Doped AlGaN/GaN 2D Electron Gas by Phonon Scattering 417 1/2 randomized collisions. As a result, one cannot make the the Fermi wave vector is proportional to ns , the result is 1/6 same simplifications for the Boltzman equation as with DP. μPE being proportional to ns . Last but not least, we But we will, as with the other scattering mechanisms, obtained the relationship between POP and ns by analyze its dependence on temperature and electron sheet determining the effect that ns has on fPOP(y) and G(k0). For density. T=300 K and the given parameters, we find that fPOP(y) is a decaying function for the given range of ns. G(k0) also has a 3. Analytical Results dependence on the electron sheet density because it is determined by using the Fang-Howard wave function.
Load more

Recommended publications
  • Room Temperature Ultrahigh Electron Mobility and Giant Magnetoresistance in an Electron-Hole-Compensated Semimetal Luptbi
    High Electron Mobility and Large Magnetoresistance in the Half-Heusler Semimetal LuPtBi Zhipeng Hou1,2, Wenhong Wang1,*, Guizhou Xu1, Xiaoming Zhang1, Zhiyang Wei1, Shipeng Shen1, Enke Liu1, Yuan Yao1, Yisheng Chai1, Young Sun1, Xuekui Xi1, Wenquan Wang2, Zhongyuan Liu3, Guangheng Wu1 and Xi-xiang Zhang4 1State Key Laboratory for Magnetism, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China 2College of Physics, Jilin University, Changchun 130023, China 3State Key Laboratory of Metastable Material Sciences and Technology, Yanshan University, Qinhuangdao 066004, China 4Physical Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia. Abstract Materials with high carrier mobility showing large magnetoresistance (MR) have recently received much attention because of potential applications in future high-performance magneto-electric devices. Here, we report on the discovery of an electron-hole-compensated half-Heusler semimetal LuPtBi that exhibits an extremely high electron mobility of up to 79000 cm2/Vs with a non-saturating positive MR as large as 3200% at 2 K. Remarkably, the mobility at 300 K is found to exceed 10500 cm2/Vs, which is among the highest values reported in three-dimensional bulk materials thus far. The clean Shubnikov-de Haas quantum oscillation observed at low temperatures and the first-principles calculations together indicate that the high electron mobility is due to a rather small effective carrier mass caused by the distinctive band structure of the crystal. Our finding provide a new approach for finding large, high-mobility MR materials by designing an appropriate Fermi surface topology starting from simple electron-hole-compensated semimetals.
    [Show full text]
  • Imperial College London Department of Physics Graphene Field Effect
    Imperial College London Department of Physics Graphene Field Effect Transistors arXiv:2010.10382v2 [cond-mat.mes-hall] 20 Jul 2021 By Mohamed Warda and Khodr Badih 20 July 2021 Abstract The past decade has seen rapid growth in the research area of graphene and its application to novel electronics. With Moore's law beginning to plateau, the need for post-silicon technology in industry is becoming more apparent. Moreover, exist- ing technologies are insufficient for implementing terahertz detectors and receivers, which are required for a number of applications including medical imaging and secu- rity scanning. Graphene is considered to be a key potential candidate for replacing silicon in existing CMOS technology as well as realizing field effect transistors for terahertz detection, due to its remarkable electronic properties, with observed elec- tronic mobilities reaching up to 2 × 105 cm2 V−1 s−1 in suspended graphene sam- ples. This report reviews the physics and electronic properties of graphene in the context of graphene transistor implementations. Common techniques used to syn- thesize graphene, such as mechanical exfoliation, chemical vapor deposition, and epitaxial growth are reviewed and compared. One of the challenges associated with realizing graphene transistors is that graphene is semimetallic, with a zero bandgap, which is troublesome in the context of digital electronics applications. Thus, the report also reviews different ways of opening a bandgap in graphene by using bi- layer graphene and graphene nanoribbons. The basic operation of a conventional field effect transistor is explained and key figures of merit used in the literature are extracted. Finally, a review of some examples of state-of-the-art graphene field effect transistors is presented, with particular focus on monolayer graphene, bilayer graphene, and graphene nanoribbons.
    [Show full text]
  • 3-July-7Pm-Resistivity-Mobility-Conductivity-Current-Density-ESE-Prelims-Paper-I.Pdf
    _____________________________________________________________________ Carrier drift Current carriers (i.e. electrons and holes) will move under the influence of an electric field because the field will exert a force on the carriers according to F = qE In this equation you must be very careful to keep the signs of E and q correct. Since the carriers are subjected to a force in an electric field they will tend to move, and this is the basis of the drift current. Figure illustrates the drift of electrons and holes in a semiconductor that has an electric field applied. In this case the source of the electric field is a battery. Note the direction of the current flow. The direction of current flow is defined for positive charge carriers because long ago, when they were setting up the signs (and directions) of the current carriers they had a 50:50 chance of getting it right. They got it wrong, and we still use the old convention! Current, as you know, is the rate of flow of charge and the equation you will have used should look like Id = nAVdq where Id = (drift) current (amperes), n = carrier density (per unit volume) A = conductor (or semiconductor) area, vd = (drift) velocity of carriers, q = carrier charge (coulombs) which is perfectly valid. However, since we are considering charge movement in an electric field it would be useful to somehow introduce the electric field into the equations. We can do this via a quantity called the mobility, where d = E In this equation: 2 -1 -1 = the drift mobility (often just called the mobility) with units of cm V s -1 E = the electric field (Vcm ) We know that the conduction electrons are actually moving around randomly in the metal, but we will assume that as a result of the application of the electric field Ex, they all acquire a net velocity in the x direction.
    [Show full text]
  • Carrier Concentrations
    2 Numerical Example: Carrier Concentrations 15 -3 Donor concentration: Nd = 10 cm Thermal equilibrium electron concentration: ≈ 15 –3 no Nd = 10 cm Thermal equilibrium hole concentration: 2 2 ⁄ ≈2 ⁄ ()10 –3 ⁄ 15 –3 5 –3 po =ni no ni Nd ==10 cm 10 cm 10 cm Silicon doped with donors is called n-type and electrons are the majority carriers. Holes are the (nearly negligible) minority carriers. EECS 105 Fall 1998 Lecture 2 Doping with Acceptors Acceptors (group III) accept an electron from the lattice to fill the incomplete fourth covalent bond and thereby create a mobile hole and become fixed negative charges. Example: Boron. B– + mobile hole and later trajectory immobile negatively ionized acceptor -3 Acceptor concentration is Na (cm ), we have Na >> ni typically and so: one hole is added per acceptor: po = Na equilibrium electron concentration is:: 2 no = ni / Na EECS 105 Fall 1998 Lecture 2 Compensation Example shows Nd > Na positively ionized donors + + As As B– − negatively ionized acceptor mobile electron and trajectory ■ Applying charge neutrality with four types of charged species: ρ () ===– qno ++qpo qNd – qNa qpo–no+Nd–Na 0 2 we can substitute from the mass-action law no po = ni for either the electron concentration or for the hole concentration: which one is the majority carrier? answer (not surprising): Nd > Na --> electrons Na > Nd --> holes EECS 105 Fall 1998 Lecture 2 Carrier Concentrations in Compensated Silicon ■ For the case where Nd > Na, the electron and hole concentrations are: 2 n ≅ ≅ i no Nd – Na and po ------------------- Nd – Na ■ For the case where Na > Nd, the hole and electron concentrations are: 2 n ≅ ≅ i p o N a – N d and n o ------------------- N a – N d Note that these approximations assume that | Nd - Na|>> ni, which is nearly always true.
    [Show full text]
  • ECE 340 Lecture 41 : MOSFET II
    ECE 340 Lecture 41 : MOSFET II Class Outline: •Mobility Models •Short Channel Effects •Logic Devices Things you should know when you leave… Key Questions • Why is the mobility in the channel lower than in the bulk? • Why do strong electric fields degrade channel mobility ? • What is the major difference between long channel and short channel MOSFETs? • How can I turn these into useful logic devices? M.J. Gilbert ECE 340 – Lecture 41 12/10/12 MOSFET Output Characteristics This makes sense based on what we already know about MOSFETs… For low drain voltages, the MOSFET looks like a resistor if the MOSFET is above threshold and depending on the value of VG. Now we can obtain the conductance of the channel… +++++++++++++ ++++ - - - - - - •But again, this is only valid in the linear regime. •We are assuming that VD << VG – VT. Depletion Region Channel Region M.J. Gilbert ECE 340 – Lecture 41 12/10/12 MOSFET Output Characteristics So we can describe the linear +++++++++++++ ++++ Pinch off regime, but how do we describe the VD saturation regime… - - - - - - • As the drain voltage is increased, the voltage across the oxide decreases near the drain end. • The resulting mobile charge also decreases in the channel Depletion Region Channel Region near the drain end. • To obtain an expression for the drain current in saturation, substitute in the saturation condition. M.J. Gilbert ECE 340 – Lecture 41 12/10/12 MOSFET Output Characteristics Let’s summarize the output characteristics for NMOS and PMOS… - - - - - - NMOS P-type Si + + + + + + + + + + + + + PMOS N-type Si M.J. Gilbert ECE 340 – Lecture 41 12/10/12 Mobility Models Let’s try a simple problem… For an n-channel MOSFET with a gate oxide thickness of 10 nm, VT = 0.6 V and Z =25 µm and a channel length of 1 µm.
    [Show full text]
  • Mechanism of Mobility Increase of the Two-Dimensional Electron Gas in Heterostructures Under Small Dose Gamma Irradiation A
    Mechanism of mobility increase of the two-dimensional electron gas in heterostructures under small dose gamma irradiation A. M. Kurakin, S. A. Vitusevich, S. V. Danylyuk, H. Hardtdegen, N. Klein, Z. Bougrioua, B. A. Danilchenko, R. V. Konakova, and A. E. Belyaev Citation: Journal of Applied Physics 103, 083707 (2008); View online: https://doi.org/10.1063/1.2903144 View Table of Contents: http://aip.scitation.org/toc/jap/103/8 Published by the American Institute of Physics Articles you may be interested in Gamma irradiation impact on electronic carrier transport in AlGaN/GaN high electron mobility transistors Applied Physics Letters 102, 062102 (2013); 10.1063/1.4792240 Influence of γ-rays on dc performance of AlGaN/GaN high electron mobility transistors Applied Physics Letters 80, 604 (2002); 10.1063/1.1445809 Two dimensional electron gases induced by spontaneous and piezoelectric polarization in undoped and doped AlGaN/GaN heterostructures Journal of Applied Physics 87, 334 (1999); 10.1063/1.371866 Annealing of gamma radiation-induced damage in Schottky barrier diodes Journal of Applied Physics 101, 054511 (2007); 10.1063/1.2435972 60 Electrical characterization of Co gamma radiation-exposed InAlN/GaN high electron mobility transistors Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena 31, 051210 (2013); 10.1116/1.4820129 Review of radiation damage in GaN-based materials and devices Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 31, 050801 (2013); 10.1116/1.4799504 JOURNAL OF APPLIED PHYSICS 103, 083707 ͑2008͒ Mechanism of mobility increase of the two-dimensional electron gas in AlGaN/GaN heterostructures under small dose gamma irradiation ͒ A.
    [Show full text]
  • Carrier Scattering, Mobilities and Electrostatic Potential in Mono-, Bi- and Tri-Layer Graphenes
    Carrier scattering, mobilities and electrostatic potential in mono-, bi- and tri-layer graphenes Wenjuan Zhu*, Vasili Perebeinos, Marcus Freitag and Phaedon Avouris** IBM Thomas J. Watson Research Center, Yorktown Heights, NY 10598, USA ABSTRACT The carrier density and temperature dependence of the Hall mobility in mono-, bi- and tri-layer graphene has been systematically studied. We found that as the carrier density increases, the mobility decreases for mono-layer graphene, while it increases for bi- layer/tri-layer graphene. This can be explained by the different density of states in mono- layer and bi-layer/tri-layer graphenes. In mono-layer, the mobility also decreases with increasing temperature primarily due to surface polar substrate phonon scattering. In bi- layer/tri-layer graphene, on the other hand, the mobility increases with temperature because the field of the substrate surface phonons is effectively screened by the additional graphene layer(s) and the mobility is dominated by Coulomb scattering. We also find that the temperature dependence of the Hall coefficient in mono-, bi- and tri-layer graphene can be explained by the formation of electron and hole puddles in graphene. This model also explains the temperature dependence of the minimum conductance of mono-, bi- and tri-layer graphene. The electrostatic potential variations across the different graphene samples are extracted. I. INTRODUCTION In the past few decades, the semiconductor industry has grown rapidly by offering every year higher function per cost. The major driving force of this performance increase is device scaling. However, scaling is becoming more and more difficult and costly as it approaches its scientific and technological limits.
    [Show full text]
  • Lecture 3 Electron and Hole Transport in Semiconductors Review
    Lecture 3 Electron and Hole Transport in Semiconductors In this lecture you will learn: • How electrons and holes move in semiconductors • Thermal motion of electrons and holes • Electric current via drift • Electric current via diffusion • Semiconductor resistors ECE 315 – Spring 2005 – Farhan Rana – Cornell University Review: Electrons and Holes in Semiconductors holes + electrons + + As Donor A Silicon crystal lattice + impurity + As atoms + ● There are two types of mobile charges in semiconductors: electrons and holes In an intrinsic (or undoped) semiconductor electron density equals hole density ● Semiconductors can be doped in two ways: N-doping: to increase the electron density P-doping: to increase the hole density ECE 315 – Spring 2005 – Farhan Rana – Cornell University 1 Thermal Motion of Electrons and Holes In thermal equilibrium carriers (i.e. electrons or holes) are not standing still but are moving around in the crystal lattice because of their thermal energy The root-mean-square velocity of electrons can be found by equating their kinetic energy to the thermal energy: 1 1 m v 2 KT 2 n th 2 KT vth mn In pure Silicon at room temperature: 7 vth ~ 10 cm s Brownian Motion ECE 315 – Spring 2005 – Farhan Rana – Cornell University Thermal Motion of Electrons and Holes In thermal equilibrium carriers (i.e. electrons or holes) are not standing still but are moving around in the crystal lattice and undergoing collisions with: • vibrating Silicon atoms • with other electrons and holes • with dopant atoms (donors or acceptors) and
    [Show full text]
  • Extrinsic Semiconductors - Mobility
    Lecture 8: Extrinsic semiconductors - mobility Contents 1 Carrier mobility 1 1.1 Lattice scattering . .2 1.2 Impurity scattering . .3 1.3 Conductivity in extrinsic semiconductors . .4 2 Degenerate semiconductors 7 3 Amorphous semiconductors 8 1 Carrier mobility Dopants in an intrinsic semiconductor perform two major functions 1. They increase carrier concentration of a particular polarity (i.e. elec- trons or holes) so that the overall conductivity is higher. Usually this is orders of magnitude higher than the intrinsic semiconductor and is dominated by either electrons or holes i.e. the majority carriers. 2. Dopants also stabilize carrier concentration around room temperature. For Si, the saturation regime extends from roughly 60 K to 560 K. Consider the general conductivity equation σ = neµe + peµh (1) For extrinsic semiconductors with either n or p much higher than the minority carrier concentration equation 1 can be written as n type : σ = neµ e (2) p type : σ = peµh 1 NOC: Fundamentals of electronic materials and devices µe and µh are the drift mobilities of the carriers. They are given by eτ µ = e e m∗ e (3) eτh µh = ∗ mh The drift mobilities are a function of temperature and in extrinsic semicon- ductors they depend on the dopant concentration. This dependence comes from the scattering time, τe and τh, which is the time between two scattering events. Another way of writing the scattering time is in terms of a scattering cross section (S). This is given by 1 τ = (4) S vth Ns where vth is the mean speed of the electrons (thermal velocity) and Ns is the number of scatters per unit volume.
    [Show full text]
  • Mobility and Saturation Velocity in Graphene on Silicon Dioxide
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Illinois Digital Environment for Access to Learning and Scholarship Repository MOBILITY AND SATURATION VELOCITY IN GRAPHENE ON SILICON DIOXIDE BY VINCENT E. DORGAN THESIS Submitted in partial fulfillment of the requirements for the degree of Master of Science in Electrical and Computer Engineering in the Graduate College of the University of Illinois at Urbana-Champaign, 2010 Urbana, Illinois Adviser: Assistant Professor Eric Pop ABSTRACT Transport properties of exfoliated graphene samples on SiO2 are examined from four- probe electrical measurements combined with electrical and thermal modeling. Data are analyzed with practical models including gated carriers, thermal generation, “puddle” charge, and Joule heating. Graphene mobility is characterized as a function of carrier density at temperatures from 300 to 500 K. In addition, electron drift velocity is obtained at high electric fields up to 2 V/μm, at both 80 K and 300 K. Mobility displays a peak vs. carrier density and decreases with rising temperature above 300 K. The drift velocity approaches saturation at fields >1 V/μm, shows an inverse dependence on carrier density (~n-1/2), and decreases slightly with temperature. Satura- tion velocity is >3×107 cm/s at low carrier density, and remains greater than in Si up to 1.2×1013 -2 cm density. Transport appears primarily limited by the SiO2 substrate, but results suggest in- trinsic graphene saturation velocity could be more than twice that observed here. ii To my grandparents for their constant support of my education iii ACKNOWLEDGMENTS I would like to thank my adviser, Professor Eric Pop, for allowing me join his research group, and more importantly, for his support and guidance during this research project.
    [Show full text]
  • Influence of Temperature to Electron Mobility on Top of Channel in 14 Nm N-Finfet
    Proceedings of the International MultiConference of Engineers and Computer Scientists 2017 Vol II, IMECS 2017, March 15 - 17, 2017, Hong Kong Influence of Temperature to Electron Mobility on Top of Channel in 14 nm n-FinFET Nuttapong Patcharasardtra, Weera Pengchan, Member, IAENG Abstract—The temperature behavior that influential to the II. THEORY electron mobility on top surface in 14 nanometer FinFET channel. The Mobility could find on I-V characterizing A. Drain current saturation simulation process and giving the result from the TCAD software by biasing on the FinFET structure with gate voltage The relationship between drain current and voltage (I-V), at 1 volt and the drain-source voltage from 0 Volt to 1 Volt to there is two states of this characteristic as linear and obtain the saturation drain current from I-V characteristic. saturation. The drain current saturation was coming with The Electron mobility was lowering by increasing the linear part of threshold voltage that bring ID from linear temperature from 303K (30°C) to 353K (80°C). This FinFET situations to saturation state and this current will not change structure gave the IDS (Sat) about 29 µA and gave mobility at VDS by the gate voltage. The saturation drain current (ID (Sat)) can 2 = 0 Volt about 575 cm /Vs, at VDS = 1 Volt, the mobility solve by (1) [3]: dramatically down to 3.4 cm2/Vs. () 2 WVVg gs ds Index Terms—FinFET, Electron Mobility, Device (1) Simulation, Temperature Effect I D() sat C OX 2m L g I. INTRODUCTION 3 he device that brings solution to be a good smaller t ox m 1 , µ is electron mobility, Cox is gate oxide T transistor in present, SOI Tri-gate FET.
    [Show full text]
  • High Electron Mobility Transistors: Performance Analysis, Research Trend and Applications
    Chapter 3 High Electron Mobility Transistors: Performance Analysis, Research Trend and Applications Muhammad Navid Anjum Aadit, Sharadindu Gopal Kirtania, Farhana Afrin, Md. Kawsar Alam and Quazi Deen Mohd Khosru Additional information is available at the end of the chapter http://dx.doi.org/10.5772/67796 Abstract In recent years, high electron mobility transistors (HEMTs) have received extensive atten‐ tion for their superior electron transport ensuring high speed and high power applica‐ tions. HEMT devices are competing with and replacing traditional field‐effect transistors (FETs) with excellent performance at high frequency, improved power density and satis‐ factory efficiency. This chapter provides readers with an overview of the performance of some popular and mostly used HEMT devices. The chapter proceeds with different struc‐ tures of HEMT followed by working principle with graphical illustrations. Device perfor‐ mance is discussed based on existing literature including both analytical and numerical models. Furthermore, some notable latest research works on HEMT devices have been brought into attention followed by prediction of future trends. Comprehensive knowl‐ edge of up‐to‐date results, future directions, and their analysis methodology would be helpful in designing novel HEMT devices. Keywords: 2DEG, heterojunction, high electron mobility, polarization, power amplifier, quantum confinement 1. Introduction The requirement of high switching speed such as needed in the field of microwave com‐ munications and RF technology urged transistors to evolve with high electron mobility and superior transport characteristics. The invention of HEMT devices is accredited to T. Mimura who was involved in research of high‐frequency, high‐speed III–V compound semiconductor devices at Fujitsu Laboratories Ltd, Kobe, Japan.
    [Show full text]