Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session M9: Semiconductor Materials: Synthesis, Growth, & Processing |
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Sponsoring Units: DCMP Chair: Dongming Mei, University of South Dakota Room: 006D |
Wednesday, March 4, 2015 11:15AM - 11:27AM |
M9.00001: Self-heating in an AlGaN/GaN transistor studied by ultraviolet and visible micro-Raman scattering Mohammad Nazari, Logan Hancock, Edwin Piner, Mark Holtz The two-dimensional electron gas (2DEG) at GaN/AlGaN interface is the basis for high electron mobility transistor. The 2DEG region forms spontaneously without any doping and is less than 10 nm in thickness. Current-induced self-heating results in large temperature rises in these devices and represents the principal limiting factor in these devices. We report direct measurements of self-heating in an AlGaN/GaN high electron mobility transistor using ultraviolet (UV) and visible micro-Raman spectroscopy. The phonon shift is used to evaluate operando temperature rise in different layers of the material stack corresponding to different depths. UV measurements, due to short optical penetration depth, give temperature rise in top 100 nm of GaN, i.e., close to the 2DEG. The visible measurements provide an average temperature rise through the 1 micron thick GaN layer and in the Si substrate close to the interface. A depth profile is developed based on the combined data sets obtained under experimentally identical conditions. Finite element thermal simulation developed based on the experimentally determined temperature-depth profile reveal thermal resistance barrier of 10$^{-8}$ K$\cdot$m$^{2}$/W at the interface between AlN and Si substrate. [Preview Abstract] |
Wednesday, March 4, 2015 11:27AM - 11:39AM |
M9.00002: Growth of high quality GaN layer on carbon nanotube-graphene network structure as intermediate layer Taeo Hoon Seo, Ah Hyun Park, Sungchan Park, Myung Jong Kim, Eun-Kyung Suh In general, high-quality GaN layers are synthesized on low-temperature (LT) GaN buffer layer on a single crystal sapphire substrate. However, large differences in fundamental properties such as lattice constants and thermal expansion coefficients between GaN layer and sapphire substrate generate high density of threading dislocation (TD) that leads to deterioration of optical and structural properties. Graphene has been attracting much attention due to its excellent physical properties However, direct epitaxial growth of GaN film onto graphene layer on substrates is not easily accessible due to the lack of chemical reactivity on graphene which consisted of C-C bond of sp$^{\mathrm{2}}$ hexagonally arranged carbon atoms with no dangling bonds. In this work, an intermediate layer for the GaN growth on sapphire substrate was constructed by inserting carbon nanotubes and graphene hybrid structure (CGH) Optical and structural properties of GaN layer grown on CGH were compared with those of GaN layer directly grown on sapphire CNTs act as nucleation sites and play a crucial role in the growth of single crystal high-quality GaN on graphene layer. Also, graphene film acts as a mask for epitaxial lateral overgrowth of GaN layer, which can effectively reduce TD density. [Preview Abstract] |
Wednesday, March 4, 2015 11:39AM - 11:51AM |
M9.00003: Crystal growth and detector performance of large size high-purity Ge crystals Guojian Wang, Mark Amman, Hao Mei, Dongming Mei, Klaus Irmscher, Yutong Guan, Gang Yang High-purity germanium crystals with 12 cm in diameter were grown in a hydrogen atmosphere using the Czochralski method. The dislocation density of the crystals was determined to be in the range of 2000 - 4200 cm$^{\mathrm{-2}}$, which meets a requirement for use as a radiation detector. The axial and radial distributions of impurities in the crystals were measured by Hall effect and Photo-thermal ionization spectroscopy (PTIS). Two detectors were also fabricated from one of the crystals with different techniques and then evaluated for electrical and spectral performance. Measurements of gamma-ray spectra from $^{\mathrm{137}}$Cs, $^{\mathrm{241}}$Am and $^{\mathrm{60}}$Co sources demonstrate that the detectors have excellent energy resolution. Keywords: High-purity germanium crystal, Czochralski method This work is supported by DOE grant DE-FG02-10ER46709 and the state of South Dakota. [Preview Abstract] |
Wednesday, March 4, 2015 11:51AM - 12:03PM |
M9.00004: Characterization of dislocation and defects for large high purity Ge crystals Hao Mei, Guojian Wang, Yutong Guan, Gang Yang, Dongming Mei Large diameter ($\sim$ 10 cm) high purity Germanium (HP-Ge) crystals have been growing via Czochralski method at University of South Dakota. We investigate the impacts of growth rate, time-temperature profile, and thermal gradient on the dislocation and defects distribution in HP-Ge crystals along \textless 100\textgreater orientation. The dislocation density across the entire cross-section of a grown crystal is measured using microscope. Utilizing X-Ray Diffraction method, we obtain the rocking curves from the same crystal samples. We analyze the correlation between the full width at half maximum (FWHM) of the rocking curves and the dislocation densities from the optical observations (etch pits distribution). A model that describes the correlation of dislocation density, along the HP-Ge crystal, with the FWHM of the rock curves for XRD is established. We report these analytic results. [Preview Abstract] |
Wednesday, March 4, 2015 12:03PM - 12:15PM |
M9.00005: The Relationship Between Terminating Oxide Chemistry and InAs (100) Two-Dimensional Electron Gas (2DEG) Conductivity Kristen Collar, Wenyuan Jiao, Jincheng Li, Wei Kong, April Brown InAs generated much interest due to its small bandgap, high electron mobility and quasi-two dimensional electron gas (2DEG) which forms at the surface of oxidized and atomically-clean InAs. Electrical characterization of the 2DEG, particularly its correlation to oxide-InAs interface states is key to understanding the factors controlling conductivity. This study perturbs the oxide formation by investigating the dominating chemical reactions yielding the heterogeneous In- and As-based native oxide. Herein, we study the relationships between the conductivity and oxide surface chemistry of 100nm InAs films terminated with In or As monolayers using Molecular Beam Epitaxy then oxidized upon exposure to air. We speculate that the observed trends in the 2DEG conductivity are due to differences in the nature of predominate defects associated with oxide chemistries and their formation. Angle-resolved X-ray photoelectron spectroscopy revealed that In oxide was dominate at all probing depths, with more As oxide at the surface. Furthermore, an increase in incorporated oxygen degraded the mobility. Thus, we show that the surface termination impacts the 2DEG mobility and carrier concentration through the extent and homogeneity of oxygen incorporation during the formation of the oxide layer. [Preview Abstract] |
Wednesday, March 4, 2015 12:15PM - 12:27PM |
M9.00006: Purification of Germanium Crystals by Zone Refinement: Theoretical and Experimental Approaches Gang Yang, Yutong Guan, Guojian Wang, Hao Mei, Fanyi Jian, Dongming Mei The results of single germanium crystals grown from zone-refined germanium ingots, identified by photon thermal ionization spectroscopy (PTIS), show that there are four main impurities, aluminum (Al), phosphor (P), boron (B) and gallium (Ga) in the crystals. Based the PTIS results, we investigated the influences of zone speed, zone width and the number of passes on effective segregation coefficient of Al, P and Ga in the process of zone refinement, then the further calculation of distribution of Al, P and Ga along the zone refined ingots has been conducted. In terms of trend of impurity distribution, the calculated results have a very good agreement with the experimental results. We report both the theoretical calculations and the experimental results. This work is supported by DOE grant DE-FG02-10ER46709 and the state of South Dakota. [Preview Abstract] |
Wednesday, March 4, 2015 12:27PM - 12:39PM |
M9.00007: Effects of Light Exposure on Dopant Incorporation and Migration in MBE-Grown GaAs(001) Charlotte E. Sanders, D.A. Beaton, K. Alberi Light-stimulated epitaxy of II-VI semiconducting materials is known to reduce crystalline defect density and enhance substitutional dopant incorporation relative to traditional ``dark'' epitaxial growth. These effects have been speculated to arise from photon-adatom interactions at the growth front, and from involvement in bonding processes by photogenerated carriers; however, a conclusive explanation of the observed effects has yet to be found. We are revisiting this topic, attempting to clarify the mechanisms of light-stimulated epitaxy and to explore its effects on the class of III-V materials. Here we report an ongoing investigation into dopant incorporation and migration in MBE-grown GaAs(001) when the growth front is irradiated during deposition. On the basis of our preliminary findings, and by comparing our new results with results previously obtained for light-stimulated effects on doping of II-VI systems, we can begin to draw conclusions about the mechanisms underlying light-stimulated epitaxy and their potential utility to MBE growth of complex multilayer structures. This work was supported by the DOE Office of Science, Basic Energy Sciences, under contract DE-AC36-08G028308. [Preview Abstract] |
Wednesday, March 4, 2015 12:39PM - 12:51PM |
M9.00008: Progress in the growth and optical properties of dilute bismide III-V semiconductor alloys Daniel A. Beaton, T. Christian, R.B. Lewis, K. Alberi, A. Mascarenhas The dilute bismuth containing III-V semiconducting alloys of have great potential for application in many areas of semiconductor technology, such as multijunction photvoltaics and solid-state lighting. There is a large reduction of the fundamental bandgap of GaAs with bismuth incorporation resultant from the raising of the valence band maximum. Dilute bismide alloys have long been compared to the dilute nitride alloy because bismuth introduces a state near the valence band edge of the host GaAs (instrad of near the conduction band edge in the nitride alloys) that affects its optical and electronic properties. Here I will discuss some recent advances in our understanding of the surface processes involved in dilute bismide alloy growth by molecular beam epitaxy which have lead to improved film quality and the growth of new bismide alloys. The improved film quality has made it possible to further explore the properties of this material. [Preview Abstract] |
Wednesday, March 4, 2015 12:51PM - 1:03PM |
M9.00009: Interplay of film thickness and laser fluence in laser-crystallized silicon films Matthew R. Semler, Justin M. Hoey, Srinivasan Guruvenket, Cody R. Gette, Orven F. Swenson, Erik K. Hobbie A detailed study of the laser crystallization of amorphous silicon thin films as a function of laser fluence and film thickness will be presented. Silicon films grown through plasma-enhanced chemical vapor deposition were crystallized with a pulsed, neodymium-doped vanadate laser, operating at 355 nm. The crystallinity, morphology, and optical and electronic properties of the films are characterized through transmission and reflectance spectroscopy, resistivity measurements, Raman spectroscopy, X-ray diffraction, atomic force microscopy, and optical and scanning-electron microscopy. The films reveal a unique surface morphology that strongly couples to the electronic characteristics of the films, with a minimum laser fluence at which the film properties are optimized. [Preview Abstract] |
Wednesday, March 4, 2015 1:03PM - 1:15PM |
M9.00010: Investigation of Nanodiamond and Silicon Carbide Foils Product for H- Stripping to Support Spallation Neutron Source Gary Harris, James Griffin, RD Vispute Diamond and silicon carbide (SiC) is an ideal material as an H- stripper foil for spallation neutron source (SNS) applications due to their high thermal conductivity, low molecular weight, and strength. Cubic silicon carbide grown on silicon is a material tension stress and the foil does not curl. Polycrystalline diamond is characterized by a high degree of internal stress, which causes the foil to curl when not supported by the substrate. the sic is grown using a RF CVD system. Hot filament chemical vapor deposition (HFCVD) was used to grow diamond on a silicon substrate. In both cases a 1.2 cm diameter window was etched in the silicon using a 1:1:3 solution of hydrofluoric, nitric, and acetic acids so that the diamond of SiC foil would be suspended while being supported on all sides by the silicon. Wax and or photoresist were used as masks to protect the outer silicon from etching. Raman spectroscopy verified the quality of the grown material. Atomic force microscopy (AFM) revealed that the diamond foil originally against the substrate had an average roughness of \textless 6.7 nm while the foil away from the substrate had an average roughness of 13.2 nm. The SiC foils had roughness less than 3 nm. Scanning electron microscopy (SEM) revealed no cracks in the suspended foil. [Preview Abstract] |
Wednesday, March 4, 2015 1:15PM - 1:27PM |
M9.00011: Synthesis and structural characterization of Nb2O5 Leonilson Kiyoshi Herval, Driele von Dreifus, Adriano C. Rabelo, Ariano D. Rodrigues, Yara Galv\~ao Gobato, Adilson J.A. de Oliveira, Ernesto C. Pereira, Marcio P.F. de Godoy Niobium and niobium alloys are used in a large number of industrial applications. Niobium Pentoxide (Niobic Anhydride, $Nb_{2}O_{5}$) is probably the commonest compound of niobium. It is a colorless insoluble solid that is fairly unreactive and it is the main precursor to all materials made of niobium with application in electronic components such as capacitor and optical glasses. In general $Nb_{2}O_{5}$ samples present many crystalline phases which are strongly dependent on the preparation parameters. We have studied two different phases (hexagonal and orthorhombic) of $Nb_{2}O_{5}$ synthesized by Pechini method and characterized them by X-Ray Diffraction (XRD), Raman spectroscopy and Magnetometry using a Superconducting Quantum Interference Device (SQUID). Our results show that the hexagonal phase dominates for samples prepared at 500$^{\circ}$C while the orthorhombic phase is increased for samples prepared at 600$^{\circ}$C. Correlation between Raman spectroscopy and XRD allowed the identification of these crystalline phases as well the study of annealing effects in-situ. Both phases are paramagnetic and the orthorhombic phase presents a significant increase of effective magnetic moments as compared to hexagonal phase. [Preview Abstract] |
Wednesday, March 4, 2015 1:27PM - 1:39PM |
M9.00012: Kondo effect in a novel 5d quasi-skutterudite Yb$_{3}$Os$_{4}$Ge$_{13}$ Youguo Shi, Chongli Yang, Xia Wang, Xu Zhang, Desheng Wu, Yifeng Yang, Jianlin Luo We report the crystal growth of a new compound, Yb$_{3}$Os$_{4}$Ge$_{13}$, by using a Bi-flux method. It crystalizes in the quasi-skutterudite-type caged structure with a cubic space group of Pm-3n (No. 223). Magnetic measurements reveal almost fully localized Yb $f$-moments above 120 K. The resistivity exhibits a crossover from metallic to insulating behavior with a logarithmic increase below $\sim$ 40 K. The specific heat coefficient shows a rapid upturn below $\sim$ 5 K and exceeds 2 J mol$^{-1}$ K$^{-2}$ at 2 K. Our experimental analysis and electronic band structure calculations demonstrate that Yb$_{3}$Os$_{4}$Ge$_{13}$ exhibits the Kondo effect due to strong hybridization of the localized Yb $f$-moments with the $p$-electrons of the surrounding Ge-cages. [Preview Abstract] |
(Author Not Attending)
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M9.00013: Formation of ST12 phase Ge nanoparticles in ZnO thin films Abdullah Ceylan, Emre Gumrukcu, Sadan Ozcan In this work, we investigate the effects of reactive and nonreactive growth of ZnO on the rapid thermal annealing (RTA) induced formation of Ge nanoparticles (Ge-np) in ZnO: Ge nanocomposite thin films. The samples were deposited by sequential sputtering of ZnO and Ge thin film layers with a total thickness of about 600 nm on Si substrates followed by an ex-situ (RTA) at 600$^{\circ}$C for 30, 60, 90, 120, 150, 180, and 210 s under forming gas atmosphere. In order for the reactive sputtering of ZnO layer, 5 mTorr Oxygen was introduced to the growth chamber. XRD and Raman analyses were utilized to investigate the effect of RTA time on the structural evolution of the samples. It has been realized that crystal structure of Ge nanoparticles is significantly affected by the growth method of the embedding ZnO layer. While reactive deposition of ZnO layers results in a mixture of diamond cubic (DC) and simple tetragonal (ST12) Ge-np, nonreactive deposition of ZnO layers leads to the formation of pure DC Ge-np upon RTA process. Formation of these two phases has been discussed based on the existence of native point defects such as oxygen vacancies and Zn interstitials. [Preview Abstract] |
Wednesday, March 4, 2015 1:51PM - 2:03PM |
M9.00014: Single Element Silicon Quasicrystal on Glass Abdul Middya Quasicrystal is an exotic form of ordering of materials structure found in nature. In this work, we report on formation of single element silicon (Si) quasicrystal, instead of metallic alloys. We found small quantity of quasicrystalline silicon on glass substrate when silicon (Si) and atomic hydrogen (H) atoms in vacuum chamber are allowed to condense on glass substrate maintained at 250$^{\circ}$C in hot wire chemical vapor deposition (hot-wire CVD) technique. We observed Penrose tiling at the surface of silicon thin-film as observed by atomic force microscopy (AFM). However, this texturing consists of six-fold symmetry and five-fold symmetry on the surface of spherical ball. We found experimental evidence of the quasi-unit cell, building blocks of quasicrystalline structure. The ordering of quasi-unit cell improves with increasing hydrogen dilution. The Raman transverse optical (TO) peak is observed at 517 cm-1, although the grain size is only 1 to 2 ?m. We also found, for the first time, direct experimental evidence of real existence of crystallographic plane in crystal structure. The micrograph of SEM shows grains appear in a very symmetric position, like diffraction spots of ceramics (alloy), we found ceramics-like silicon thin-film. [Preview Abstract] |
Wednesday, March 4, 2015 2:03PM - 2:15PM |
M9.00015: Increasing The Efficiency of Silicon Solar Cells via an Anti-reflecting Nano-porous Surface Layer Ahmet Coskuner, Aisha Gokce, Omer Altunay, Yani Skarlatos, Ozhan Ozatay Electrochemical etching of silicon in a controlled environment results in a porous surface that has many application areas from drug delivery to optoluminescent devices. There is vast interest in implementing porous silicon in silicon solar cells to increase light absorption and therefore the efficiency. Here we demonstrate successful formation of a nano-porous surface on mono-crystalline Si wafers as well as doped Si solar cells. Our results show that pre-cleaning and post-drying is crucial to acquire a smooth, non-cracked topography. We also find that under similar conditions, smaller pores in a denser arrangement and with shorter depths form in p-n junction type Si wafers compared to n-type or p-type Si. In ITO coated porous Si solar cells with Al back contacts, the measured efficiency increase is almost 50{\%} of those without a porous surface. This is a promising result to further enhance the performance of Si solar cell devices. [Preview Abstract] |
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