Growthmechanismand Characteristics of Semiconductor Nanowires For
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www.symbiosisonline.org Symbiosis www.symbiosisonlinepublishing.com Research Article Nanoscience & Technology: Open Access Open Access Growth Mechanism and Characteristics of Semiconductor Nanowires for Photonic Devices N. B Singh1, S. R Coriell1, Matthew King2, Brian Wagner2, David Kahler2, David Knuteson2, Andre Berghman2 and Sean McLaughlin2 1University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250 2Northrop Grumman Corporation ES, 1212 Winterson Road, Linthicum, MD 21250 Received: March 31, 2014; Accepted: April 27, 2014; Published: April 29, 2014 *Corresponding author: N. B Singh, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250 photodiodes (A Abstract photon counting applications. These arecapable of low-light An overview on the growth mechanism of nanowire, fabrication detectionand havePDs) great are potentialvery capable for the detectors variety ofin applications. finding and and performance of selenide nanowires devices is presented. Growth of nano particles and preliminary results on the formation Binary, ternary and quaternary selenides have relatively low optical of nanowires of lead selenide is reported. Results are presented for the zinc selenide nanowire based devices, performance and combination of properties of selenides makes them very important materialsabsorption for coefficient detector andapplications. have wide Lead transparency selenide (PbSe)range. nanoThis particles and nanowires were grown by the physical vapor transport to device arrays. (PVT) method and zinc selenide (ZnSe) nanowire was grown by more specifically the ability to transition from single NW devices chemical vapor transport (CVT) methods. Observations on the growth Experimental Method of PbSe indicate that oriented attachment of nanocrystal building Materials purification blocks produces nanowires. On silicon (111) substrates binding was observed to be on (001) and (111) faces. Zinc selenide nanowires As supplied PbSe and ZnSe materials had listed purity of were fabricated into nano Avalanche Photodiodes (Nano-APDs) structure. Experimental results on the fabricated devices of zinc transport method in a cleaned quartz tube in vacuum. We have used99.995%. both horizontalThese materials and vertical were geometry. purified Weby alwaysphysical observed vapor selenide show significant enhancement in photoconductivity. Growth dark residue left behind after evaporation. In order to ensure to fabricationof nanowire still and remains fabrication a big ofchallenge. devices has progressed significantly avoid the moisture we heated samples at 120oC before starting and has shown significant improvements in the performance, but 0C Keywords: PbSe; ZnSe; Nanowire growth; Vapor deposition; Photodetector; Fabrication in vacuum. the purification. The evaporation temperature was above 300 Nanowire growth Introduction We have used both physical vapor transport (PVT) and The emergence of nanotechnology has provided a great chemical vapor transport (CVT) growth methods for the growth deal of promise for the area of low light collection due to small of nanoparticles and nanowires. Details of these methods are size and hence decreased dark current. Since applications of described by authors elsewhere [7-8]. A limited number of nano-APDs in the short wavelength infrared (SWIR) region has growth experiments were performed using vapor-liquid-solid method similar to method described by Cho et al [9] to compare with PVT results. Before starting the growth, the vacuum advantagesgained a lot ofover momentum, traditional significant night vision progress equipment has been whichmade [1-7] by several research groups. Nano-APDs have significant eliminate oxygen contamination. For the growth of lead selenide range out to a wavelength of 1 µm. The near-infrared (NEIR) to nanoparticlessystem was sufficiently physical vaporpumped transport and purged growth prior was to growthused at toa mid-wavegenerally amplifiesinfrared (MWIR) radiation µm over region the is visible an excellent and near choice infrared since oC to 400oC and for nanowires it extends beyond the cutoff of silicon detectors. In GaAs, PbS, and oC. Silicon wafers (111) PbSe based detectors cover short wave infrared (SWIR), NEIR withsource thermal temperature oxide with range gold of catalyst300 were used as substrates for and MWIR region. But there is a big gap between the MWIR and temperature was maintained below 300 long wave infrared (LWIR) region. High gain and fast response we used commercial DENTON evaporator. However for the PVT time of APDs is required for variety of applications. NWs have andPbSe vapor-liquid-solid system. For the large and area smaller silicon diameter wafers substrates (>3inch diameter) (<1inch shown promising optical properties, including high transparency silicon) a three zonehorizontal transparent glass furnace was and a high order of magnitude better photocurrent. Avalanche used. Symbiosis Group *Corresponding author email: Growth Mechanism and Characteristics of Semiconductor Nanowires for Photonic Copyright: Devices © 2014 Singh et al. The growth chamber is described in Matthew R et al. [7] and Results and Discussion is shown in Figure 1. For the case of ZnSe Source temperatures It is well established that nucleation produces the desired ranged from 750°C -1000°C, while the substrate temperature shapes, and size can be controlled by controlling the growth rate range was 675°C -925°C. Argon gas was used to purge the growth and temperature, in the case of pure and doped lead selenide chamber. For the understanding the growth morphology and transition to nanocubes has added another complexity for dimension of the nanowirewe used a partial pressure range of achieving the desired sizes of nanowire for fabrication. In order Argon between 250mTorr – 760Torr. Sapphire substrates were to understand this in details we describe the growth mechanism used for ZnSe growth. Typical cleaning procedures were used of nanowires. to prepare the substrates for growth. Gold catalysts were then deposited on the substrates and the diameter for the catalyst was Growth mechanism of nanowires in the range of 10-50nm. Characterization and fabrication nanowires with any theory since impingement of atoms on substrates,It is extremely nucleating difficult agent, tipto shape,compare anisotropy growth interactionresults of X-ray characterization was performed for Omega-2 The of one nanowire and several other parameters affect the growth ta scan to determine the NW peak positions. We used a Bede rate and morphology. The classical model of whisker growth D1 x-ray diffractometer equipped with a micro source and a was based on impingement of atoms on the whisker sides, and triple-bounce Ge crystal beam conditioner. The quality and the diffusion of these adatoms to the whisker tip where they are orientation of the material were determined by X-ray rocking incorporated in the growing whisker. The vapor-liquid-solid curve and composition was determined by XPS. It was very (VLS) method used a liquid drop at the whisker tip which was an clear that PVT process produces much better materials than effective method of capturing atoms from the vapor. Parker et al vapor-solution-solid growth methods since impurities of the [10] and Givargizov et al [11] have measured L(t) as a function solution affect the growth. The morphology of nano structure was studied using a Hitachi FE-SEM equipped with a PGT EDS. Optical morphology was studied using a microscope coupled to of time t for a fixed whisker radius r. For nanowires it is clearly A typical measurement consists of carrying out an experiment an Ocean Optics USB4000-XR for determining the transmission difficult to measure L(t) during a growth experiment. properties of single wire. Photoluminescence was studied using the nanowire length L as a function of the nanowire radius r. 266 nm light source. Performance of the fabricated nanowire Johanssonfor a fixed timeet al.[12] and after used stopping this method the growthfor data process, on GaP measuringnanowires devices were evaluatedby current-voltage data in the range of -20 to 20V. A 150W broadband halogen light was used as a source Johansson et al. [12] also present a simple mass transport model on the device through the microscope objective on the probe ofand nanowire Schmidt growth.et al [13] The used model the method includes for impingement Si nanowires of studies. atoms station. Current-voltage curve was used to determine the ratio of on the substrate, on the nanowire sides, and on the liquid drop. photocurrent to dark current for each NW device. The atoms on the substrate diffuse [14] to the whisker base and Temperature Condensation ΔT Sublimation xsubstrate xsource Position in Furnace Substrate + Au Catalysts Heater Coils Quartz Tube Gas Flow Source Vapor Source Material Substrate Al O Crucible 2 3 Figure 1: achieve the size of the nanowires. Schematic of Nano wire growth furnace is described by King et al [7] in details for controlling the thermal profile, vapor pressure and to Citation: Singh NB, Coriell SR, King M, Wagner B, Kahler D, et al. (2014) Growth Mechanism and Characteristics of Semiconductor Page 2 of 8 Nanowires for Photonic Devices. Nanosci Technol 1(2): 1-8. Growth Mechanism and Characteristics of Semiconductor Nanowires for Photonic Copyright: Devices © 2014 Singh et al. then along the whisker sides to the liquid drop where they are Eq. (1) so it has the form incorporated into the nanowire. Johansson et al. [14] also present 1 dL a simple