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SiC Power MOSFET with Improved Gate Dielectric

Description: In this STTR program, Structured Materials Industries (SMI), and Cornell University are developing novel gate oxide technology, as a critical enabler for silicon carbide (SiC) devices. SiC is a wide bandgap semiconductor material, with many unique properties. SiC devices are ideally suited for high-power, highvoltage, high-frequency, high-temperature and radiation resistant applications. The DOE has expressed interest in developing SiC devices for use in extreme environments, in high energy physics applications and in power generation. The development of transistors based on the Metal Oxide Semiconductor Field Effect Transistor (MOSFET) structure will be critical to these applications.
Date: August 23, 2010
Creator: Sbrockey, Nick M; Tompa, Gary S; Spencer, Michael G & Chandrashekhar, Chandra MVS
Partner: UNT Libraries Government Documents Department

Low Cost Production of InGaN for Next-Generation Photovoltaic Devices

Description: The goal of this project is to develop a low-cost and low-energy technology for production of photovoltaic devices based on InGaN materials. This project builds on the ongoing development by Structured Materials Industries (SMI), of novel thin film deposition technology for Group III-Nitride materials, which is capable of depositing Group-III nitride materials at significantly lower costs and significantly lower energy usage compared to conventional deposition techniques. During this project, SMI demonstrated deposition of GaN and InGaN films using metalorganic sources, and demonstrated compatibility of the process with standard substrate materials and hardware components.
Date: July 9, 2012
Creator: Nick M. Sbrockey, Shangzhu Sun, Gary S. Tompa,
Partner: UNT Libraries Government Documents Department

Metallization and Modification of Low-k Dielectric Materials

Description: Aluminum was deposited onto both Teflon AF and Parylene AF surfaces by chemical vapor deposition of trimethylaluminum. This work shows that similar thin film (100 Angstroms) aluminum oxide adlayers form on both polymers at the low temperature dosing conditions used in the studies. Upon anneal to room temperature and above, defluorination of the polymer surfaces increased and resulted in fluorinated aluminum oxide adlayers; the adlayers were thermally stable to the highest temperatures tested (600 K). Angle-resolved spectra showed higher levels of fluorination toward the polymer/adlayer interface region. Copper films were also deposited at low temperature onto Teflon AF using a copper hexafluoroacetylacetonate-cyclooctadiene precursor. Annealing up to 600 K resulted in the loss of precursor ligands and a shift to metallic copper. As with aluminum adlayers, some polymer defluorination and resulting metal (copper) fluoride was detected. Parylene AF and polystyrene films surfaces were modified by directly dosing with water vapor passed across a hot tungsten filament. Oxygen incorporation into polystyrene occurred exclusively at aromatic carbon sites, whereas oxygen incorporation into parylene occurred in both aromatic and aliphatic sites. Oxygen x-ray photoelectron spectra of the modified polymers were comparable, indicating that similar reactions occurred. The surface oxygenation of parylene allowed enhanced reactivity toward aluminum chemical vapor deposition. Silicon-carbon (Si-Cx) films were formed by electron beam bombardment of trimethylvinylsilane films which were adsorbed onto metal substrates at low temperatures in ultra-high vacuum. Oxygen was also added to the films by coadsorbing water before electron beam bombardment; the films were stable to more than 700 K, with increasing silicon-oxygen bond formation at elevated temperatures. Copper metal was sputter deposited in small increments onto non-oxygenated films. X-ray photoelectric spectra show three-dimensional copper growth (rather than layer-by-layer growth), indicating only weak interaction between the copper and underlying films. Annealing at elevated temperatures caused coalescence or growth ...
Date: December 2008
Creator: Martini, David M.
Partner: UNT Libraries

A Scanning Tunneling Microscopy Study of As/Ge(mnn) and P/Ge(mnn) Surfaces

Description: Ge(mnn) surfaces between (100) and (111) were annealed under either arsine or phosphine in a metal-organic chemical vapor deposition chamber, then imaged with a scanning tunneling microscope. In general, arsine-exposed Ge surfaces are facetted, while phosphine-exposed surfaces remain flat. For the arsine-exposed Ge surfaces, four stable facetting directions have been identified: (100), (11,3,3), (955), and (111).
Date: November 14, 2000
Creator: McMahon, W.E. & Olsen, J.M.
Partner: UNT Libraries Government Documents Department

MOCVD Growth of AlGaInN for UV Emitters

Description: Issues related to the growth of nitride-based UV emitters are investigated in this work. More than 100 times of improved in the optical efficiency of the GaN active region can be attained with a combination of raising the growth pressure and introducing a small amount of indium. The unique issue in the UV emitter concerning the use of AlGaN for confinement and the associated tensile cracking is also investigated. They showed that the quaternary AlGaInN is potentially capable of providing confinement to GaN and GaN:In active regions while maintaining lattice matching to GaN, unlike the AlGaN ternary system.
Date: July 7, 1999
Creator: Crawford, Mary & Han, Jung
Partner: UNT Libraries Government Documents Department

Enhanced-Depletion-Width GaInNAs Solar Cells Grown by Molecular-Beam Epitaxy

Description: The 3-junction, GaInP2/GaAs/Ge solar cell is a non-optimized structure due to excess light falling on the Ge junction. Because of this, a fourth junction inserted between the GaAs and Ge subcells could use the excess light and provide an increase in device efficiency. Unfortunately, the leading candidate material, GaInNAs, suffers from very low minority-carrier diffusion lengths compared to its parent compound, GaAs. These low diffusion lengths do not allow for the collection of adequate current to keep the overall 4-junction structure current matched. If the currents generated from the GaInNAs subcell are increased, the possibility exists for practical efficiencies of greater than 40% from this structure.
Date: January 1, 2005
Creator: Ptak, A. J. & Friedman, D. J.
Partner: UNT Libraries Government Documents Department

Defect Trapping in InGaAsN Measured by Deep-Level Transient Spectroscopy

Description: Deep-level defects in p-type InGaAsN films grown by metal-organic chemical vapor deposition and molecular-beam epitaxy are investigated by deep-level transient spectroscopy (DLTS). A series of as-grown samples having varying N and In composition showed a deep hole trap with an activation energy ranging from 0.6 to 0.8 eV and an electron trap with an activation energy ranging from 0.1 to 0.4 eV. The electron trap activation energy decreased with increasing N content. Optical DLTS measurements similarly revealed the shallow electron traps, but did not show the deeper hole-trap peaks. A deep electron trap was detected when using forward bias to inject electrons during pulse filling. Together, the deep electron trap and deep hole trap may form a recombination center. This also suggests that generated carriers could recombine quickly, and therefore, such a recombination center may have prevented a deep-trap signal during optical DLTS.
Date: May 1, 2003
Creator: Johnston, S. W.; Ahenkiel, R. K.; Ptak, A. J.; Friedman, D. J. & Kurts, S. R.
Partner: UNT Libraries Government Documents Department

Defects in GaInNAs: What We've Learned So Far

Description: We show results from a number of experimental and theoretical investigations on GaInNAs in an attempt to provide a more complete picture of defects in this material than is currently available. Much has been learned in recent years, including the effects of impurities such as hydrogen and carbon, the behavior of GaInNAs on annealing, and the defects that cause a degradation of material properties, including photoluminescence intensity and, especially important for solar cells, minority-carrier lifetimes. Much of our current understanding stems from a comparison of GaInNAs grown by both MOCVD and MBE. This comparison, along with the use of several characterization techniques and theoretical modeling, has allowed us to understand the roles of various defects and to identify a signature for the defect that reduces the minority-carrier lifetime.
Date: May 1, 2003
Creator: Ptak, A. J.; Kurtz, S.; Johnston, S. W.; Friedman, D. J.; Geisz, J. F.; Olson, J. M. et al.
Partner: UNT Libraries Government Documents Department

AlGaN Materials Engineering for Integrated Multi-Function Systems

Description: This LDRD is aimed to place Sandia at the forefront of GaN-based technologies. Two important themes of this LDRD are: (1) The demonstration of novel GaN-based devices which have not yet been much explored and yet are coherent with Sandia's and DOE's mission objectives. UV optoelectronic and piezoelectric devices are just two examples. (2) To demonstrate front-end monolithic integration of GaN with Si-based microelectronics. Key issues pertinent to the successful completion of this LDRD have been identified to be (1) The growth and defect control of AlGaN and GaN, and (2) strain relief during/after the heteroepitaxy of GaN on Si and the separation/transfer of GaN layers to different wafer templates.
Date: January 1, 2001
Partner: UNT Libraries Government Documents Department

The Morphology and Microstructure of Thin-Film GaAs on Mo Substrates

Description: The growth of GaAs thin films on Molybdenum foils was investigated in an attempt to find a low-cost substrate for GaAs. The films were grown by metalorganic chemical vapor deposition (MOCVD). The film thickness was in the 2-4{micro}m range, while the deposition temperature was in the 650-825 C range. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the film morphology and microstructure, respectively. The film morphology in general, and the grain size in particular, were found to be strongly dependent on the growth temperature. However, the defect structure observed in these films was relatively insensitive to the growth conditions.
Date: April 26, 1999
Creator: Jones, K. M.; Al-Jassim, M. M.; Hasoon, F. S. (National Renewable Energy Laboratory) & Venkatasubramanian, R. (Research Triangle Institute)
Partner: UNT Libraries Government Documents Department

The Growth of InGaAsN for High Efficiency Solar Cells by Metalorganic Chemical Vapor Deposition

Description: InGaAsN alloys are a promising material for increasing the efficiency of multi-junction solar cells now used for satellite power systems. However, the growth of these dilute N containing alloys has been challenging with further improvements in material quality needed before the solar cell higher efficiencies are realized. Nitrogen/V ratios exceeding 0.981 resulted in lower N incorporation and poor surface morphologies. The growth rate was found to depend on not only the total group III transport for a fixed N/V ratio but also on the N/V ratio. Carbon tetrachloride and dimethylzinc were effective for p-type doping. Disilane was not an effective n-type dopant while SiCl4 did result in n-type material but only a narrow range of electron concentrations (2-5e17cm{sup -3}) were achieved.
Date: September 16, 1999
Partner: UNT Libraries Government Documents Department

Electron Microscopy Studies of GaP(N,As) Grown on Si

Description: The objective of this work is to perform transmission electron microscopy (TEM) studies of GaP(N,As) alloys grown by metal-organic chemical vapor deposition (MOCVD) on Si substrates. These alloys are of interest for the fabrication of high-efficiency tandem solar cells based on Si. The results indicated that the nucleation and growth conditions used are critical for obtaining planar epitaxial layers with a low defect density. In particular, antiphase domains are eliminated using a low growth temperature. TEM studies of these alloy layers, which contain only a few percent N, revealed no phase separation. However, electron diffraction studies revealed the first evidence of CuPt-type atomic ordering in these P-rich, dilute nitride alloy layers.
Date: January 1, 2005
Creator: Norman, A. G.; Geisz, J. F.; Olson, J. M.; Jones, K. M. & Al-Jassim, M. M.
Partner: UNT Libraries Government Documents Department

Evidence of the Meyer-Neldel Rule in InGaAsN Alloys: Consequences for Photovoltaic Materials; Preprint

Description: We present data showing the potential adverse effects on photovoltaic device performance of all traps in InGaAsN. Deep-level transient spectroscopy measurements were performed on InGaAsN samples grown by both metal-organic chemical vapor deposition and RF plasma-assisted molecular-beam epitaxy. For each growth technique, we studied samples with varying nitrogen composition ranging from 0% to 2.2%. A deep hole trap with activation energy ranging between 0.5 and 0.8 eV is observed in all samples. These data clearly obey the Meyer-Neldel rule, which states that all traps have the same emission rate at the isokinetic temperature. A fit of our trap data gives an isokinetic temperature of 350 K, which means that both deep and shallow traps emit slowly at the operating temperature of solar cells-thus, the traps can be recombination centers.
Date: April 1, 2003
Creator: Johnston, S. W. & Crandall, R. S.
Partner: UNT Libraries Government Documents Department

Alternative heterojunction partners for CIS-based solar cells: Annual subcontract report, 29 December 1997--28 December 1998

Description: The focus of the Phase 1 effort concerned further development of ZnO buffer layers. This work included further optimization of the metal-organic chemical vapor deposition (MOCVD) growth process and investigations of the interaction of zinc and oxygen with the absorber layers. Although much of the work had been done with Siemens' CIS material prior to this reporting period, a process for growing ZnO buffer layers on Siemens' CIGSS absorber had not been developed. The authors determined that a two-step procedure involving raising the substrate temperature to 250 C in nitrogen and then growing the buffer layer at 100 C works well with CIGSS material. Through collaboration with the Institute of Energy Conversion (IEC), completed cells with efficiencies in the 11% to 12% range were fabricated with the following structure: RF n-ZnO/i-ZnO/CIGSS. Cells with this structure were included as part of the Transient team studies. Cells were subjected to dark storage at 80 C, followed by a light soak at 40 C at IEC. Illuminated I-V curves taken at each stage of the study determined that these cells do not degrade under dark-storage conditions, which had been observed for Siemens cells with CdS buffer layers. To understand the reaction of zinc and oxygen with the absorber layers, secondary ion mass spectroscopy (SIMS) depth concentration profiles were obtained for i-ZnO/CIS structures through collaboration with Angus Rockett at the University of Illinois. SIMS profiles were obtained for ZnO films grown on polycrystalline CIS and epitaxial CIS films grown on GaAs. Comparison of the profiles strongly suggests that zinc and oxygen diffuse into the CIS along grain boundaries during the MOCVD growth process. It is also proposed that excess zinc along grain boundaries may result in the grain boundaries being n-type, which can result in enhanced loss currents. This model is consistent with the ...
Date: February 28, 2000
Creator: Olsen, L. C.
Partner: UNT Libraries Government Documents Department

Processing of CuInSe{sub 2}-based solar cells: Characterization of deposition processes in terms of chemical reaction analyses. Phase 2 Annual Report, 6 May 1996--5 May 1997

Description: This report describes research performed by the University of Florida during Phase 2 of this subcontract. First, to study CIGS, researchers adapted a contactless, nondestructive technique previously developed for measuring photogenerated excess carrier lifetimes in SOI wafers. This dual-beam optical modulation (DBOM) technique was used to investigate the differences between three alternative methods of depositing CdS (conventional chemical-bath deposition [CBD], metal-organic chemical vapor deposition [MOCVD], and sputtering). Second, a critical assessment of the Cu-In-Se thermochemical and phase diagram data using standard CALPHAD procedures is being performed. The outcome of this research will produce useful information on equilibrium vapor compositions (required annealing ambients, Sex fluxes from effusion cells), phase diagrams (conditions for melt-assisted growth), chemical potentials (driving forces for diffusion and chemical reactions), and consistent solution models (extents of solid solutions and extending phase diagrams). Third, an integrated facility to fabricate CIS PV devices was established that includes migration-enhanced epitaxy (MEE) for deposition of CIS, a rapid thermal processing furnace for absorber film formation, sputtering of ZnO, CBD or MOCVD of CdS, metallization, and pattern definition.
Date: October 20, 1999
Creator: Anderson, T.
Partner: UNT Libraries Government Documents Department

p-Type ZnO Thin Films Grown by MOCVD

Description: ZnO has demonstrated a possibility to be doped as a p-type by using nitrogen and other group-V elements. A high nitrogen doping concentration by metalorganic chemical vapor deposition (MOCVD) with nitric oxide (NO) gas has been achieved. However, the processing window for obtaining the p-type ZnO:N film is very narrow, and the hole concentration is typically low. Possible compensation and passivation effects have been studied. Hydrogen and carbon elements are detected by secondary-ion mass spectroscopy (SIMS). Considering the other experimental and modeling results, we believe that the impurities inadvertently incorporated with the zinc precursor could be compensating or passivating the nitrogen acceptor and result in the low hole concentration.
Date: February 1, 2005
Creator: Li, X.; Asher, S. E.; Keyes, B. M.; Moutinho, H. R.; Luther, J. & Coutts, T. J.
Partner: UNT Libraries Government Documents Department

Deep-Level Transient Spectroscopy in InGaAsN Lattice-Matched to GaAs: Preprint

Description: This conference paper describes the deep-level transient spectroscopy (DLTS) measurements have been performed on the quaternary semiconductor InGaAsN. A series of as-grown, metal-organic chemical vapor deposited samples having varying composition were grown and measured. A GaAs sample was used as a baseline for comparison. After adding only In to GaAs, we did not detect significant additional defects; however, adding N and both N and In led to larger hole-trap peaks and additional electron-trap peaks in the DLTS data. The samples containing about 2% N, with and without about 6% In, had electron traps with activation energies of about 0.2 and 0.3 eV. A sample with 0.4% N had an electron trap with an activation energy of 0.37 eV.
Date: May 1, 2002
Creator: Johnston, S. W.; Ahrenkiel, R. K.; Friedman, D. J. & Kurtz, S. R.
Partner: UNT Libraries Government Documents Department