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Photocarrier relaxation in the quantum kinetics regime

Description: We present a study of carrier relaxation in GaAs in the quantum- kinetics regime. The results cannot be explained by Bolzmann kinetics. They are in satisfactory agreement with quantum-kinetic theory calculation of the occupation number in k-space.
Date: November 1, 1995
Creator: Bar-Ad, S.; Kner, P.; Chemla, D.S. & El Sayed, K.
Partner: UNT Libraries Government Documents Department

Fundamental surface chemistry of GaAs OMVPE

Description: Organometallic and hydride compounds are widely used as precursors for the epitaxial growth of GaAs and other compound semiconductors. These precursors are most commonly used to perform organometallic vapor phase epitaxy (OMVPE) and also in related deposition techniques such as atomic layer epitaxy (ALE) and metalorganic molecular beam epitaxy (MOMBE). We have investigated the surface chemical properties of these precursors on GaAs(100) using a variety of surface science diagnostics. Results have shed light on the mechanisms of precursor decomposition which lead to film growth and carbon doping. For instance, kinetics of trimethylgallium (TMGa) decomposition on the Ga-rich and As-rich surfaces, measured by TPD, are in semiquantitative agreement with ALE results; indicating that the dominant growth mechanism during ALE is heterogeneous. Furthermore, there is no compelling evidence for the production of methane (CH{sub 4}) on the GaAs surface when TMGa and arsine (AsH{sub 3}) are coadsorbed.
Date: May 1, 1995
Creator: Creighton, J.R. & Truong, C.M.
Partner: UNT Libraries Government Documents Department

Photoluminescence Investigations of InGaAsN Alloys Lattice-Matched to GaAs

Description: InGaAsN is a semiconductor alloy system with the property that the inclusion of only 2% nitrogen reduces the bandgap by more than 30%. In this paper, we have measured the conduction-band mass measurements by three different techniques for 2% nitrogen in InGaAsN lattice matched to GaAs. Additionally, we also report pressure dependent measurements of the conduction-band mass between ambient and 40 kbar. Based on our results, we suggest that the observed changes in masses are a result of {Lambda}-X mixing.
Date: June 1, 1999
Creator: Jones, E.D.; Modine, N.R.; Allerman, A.A.; Fritz, I.J.; Kurtz, S.R.; Wright, A.F. et al.
Partner: UNT Libraries Government Documents Department

Nucleation and Growth of GaN on GaAs (001) Substrates

Description: The nucleation of GaN thin films on GaAs is investigated for growth at 620 "C. An rf plasma cell is used to generate chemically active nitrogen from N<SUB>2</SUB>. An arsenic flux is used in the first eight monolayer of nitride growth to enhance nucleation of the cubic phase. Subsequent growth does not require an As flux to preserve the cubic phase. The nucleation of smooth interfaces and GaN films with low stacking fault densities is dependent upon relative concentrations of active nitrogen species in the plasma and on the nitrogen to gallium flux ratio.
Date: May 3, 1999
Creator: Drummond, Timothy J.; Hafich, Michael J.; Heller, Edwin J.; Lee, Stephen R.; Liliental-Weber, Zuzanna; Ruvimov, Sergei et al.
Partner: UNT Libraries Government Documents Department

Effect of Inert Gas Additive Species on Cl(2) High Density Plasma Etching of Compound Semiconductors: Part 1. GaAs and GaSb

Description: The role of the inert gas additive (He, Ar, Xe) to C12 Inductively Coupled Plasmas for dry etching of GaAs and GaSb was examined through the effect on etch rate, surface roughness and near-surface stoichiometry. The etch rates for both materials go through a maximum with Clz 0/0 in each type of discharge (C12/'He, C12/Ar, C12/Xc), reflecting the need to have efficient ion-assisted resorption of the etch products. Etch yields initially increase strongly with source power as the chlorine neutral density increases, but decrease again at high powers as the etching becomes reactant-limited. The etched surfaces are generally smoother with Ax or Xe addition, and maintain their stoichiometry.
Date: December 23, 1998
Creator: Abernathy, C.R.; Cho, H.; Hahn, Y.B.; Hays, D.C.; Jung, K.B.; Pearton, S.J. et al.
Partner: UNT Libraries Government Documents Department

Simple intrinsic defects in GaAs : numerical supplement.

Description: This Report presents numerical tables summarizing properties of intrinsic defects in gallium arsenide, GaAs, as computed by density functional theory. This Report serves as a numerical supplement to the results published in: P.A. Schultz and O.A. von Lilienfeld, 'Simple intrinsic defects in GaAs', Modelling Simul. Mater. Sci Eng., Vol. 17, 084007 (2009), and intended for use as reference tables for a defect physics package in device models. The numerical results for density functional theory calculations of properties of simple intrinsic defects in gallium arsenide are presented.
Date: April 1, 2012
Creator: Schultz, Peter Andrew
Partner: UNT Libraries Government Documents Department

Theory of gain in group-III nitride lasers

Description: A microscopic theory of gain in a group-III nitride quantum well laser is presented. The approach, which treats carrier correlations at the level of quantum kinetic theory, gives a consistent account of plasma and excitonic effects in an inhomogeneously broadened system.
Date: June 1, 1997
Creator: Chow, W.W.; Wright, A.F. & Girndt, A.
Partner: UNT Libraries Government Documents Department


Description: We have used Coherent Bragg Rod Analysis (COBRA) to investigate the atomic structure of a 5.6 nm thick Gd{sub 2}O{sub 3} film epitaxially grown on a (100) GaAs substrate. COBRA is a method to directly obtain the structure of systems periodic in two-dimensions by determining the complex scattering factors along the substrate Bragg rods. The system electron density and atomic structure are obtained by Fourier transforming the complex scattering factors into real space. The results show that the stacking order of the first seven Gd{sub 2}O{sub 3} film layers resembles the stacking order of Ga and As layers in GaAs then changes to the stacking order of cubic bulk Gd{sub 2}O{sub 3}. This behavior is distinctly different from the measured stacking order in a 2.7 nm thick Gd{sub 2}O{sub 3} in which the GaAs stacking order persists throughout the entire film.
Date: December 6, 2002
Partner: UNT Libraries Government Documents Department

Device Technology Investigation: Subsystems Packaging Study: Feasibility of PCSS - Based Pulser for Highly Portable Platforms

Description: This report summarizes an investigation of the use of high-gain Photo-Conductive Semiconductor Switch (PCSS) technology for a deployable impulse source. This includes a discussion of viability, packaging, and antennas. High gain GaAs PCSS-based designs offer potential advantages in terms of compactness, repetition rate, and cost.
Date: July 1, 2002
Partner: UNT Libraries Government Documents Department

Advances in oxide-confined vertical cavity lasers

Description: We review the advances made in device fabrication, structure, and performance of vertical-cavity surface emitting lasers (VCSELs) which incorporate the selective oxidation of AlGaAs.
Date: February 1, 1996
Creator: Choquette, K.D.; Schneider, R.P. Jr.; Lear, K.L.; Geib, K.M.; Hou, H.Q.; Chui, H.C. et al.
Partner: UNT Libraries Government Documents Department

Sputtering induced changes in defect morphology and dopant diffusion for Si implanted GaAs: Influence of ion energy and implant temperature

Description: Experimental observations of dopant diffusion and defect formation are reported vs ion energy and implant temperature in Si-implanted GaAs. In higher energy implants (>100 keV), little or no diffusion occurs, while at energies less than 100 keV, the amount of dopant redistribution is inversely proportional to energy. Extended defect density shows the opposite trend, increasing with ion energy. Similarly, Si diffusion during post implant annealing decreases by a factor of 2.5 as the implant temperature increases from -2 to 40 C. In this same temperature range, maximum depth and density of extrinsic dislocation loops increases by factors of 3 and 4, respectively. Rutherford backscattering channeling indicates that Si- implanted GaAs undergoes an amorphous-to-crystalline transition at Si implant temperatures between -51 and 40 C. A unified explanation of the effects of ion energy and implant temperature on both diffusion and dislocation formation is proposed based on known differences in sputter yields between low and high energy ions and crystalline and amorphous semiconductors. The model assumes that the sputter yield is enhanced at low implant energies and by amorphization, thus increasing the excess vacancy concentration. Estimates of excess vacancy concentration are obtained by simulations of the diffusion profiles and are quantitatively consistent with a realistic sputter yield enhancement. Removal of the vacancy-rich surface by etching prior to annealing completely suppresses the Si diffusion and increases the dislocation density, lending further experimental support to the model.
Date: December 1, 1994
Creator: Robinson, H.G.; Deal, M.D.; Lee, C.C.; Haynes, T.E.; Allen, E.L. & Jones, K.S.
Partner: UNT Libraries Government Documents Department

Non-destructive inter-level dielectric via in-line process monitoring by atomic force microscopy

Description: A new application using atomic force microscopy (AFM) for in-line process control monitoring (PCM) of an interlevel dielectric via etching step is reported. The AFM with its near atomic-level resolution is capable of nondestructively measuring whether micron-sized vias have been etched to completion. Etch completion is determined by comparing the AFM measured etch depth of adjacent via holes through {approximately}4000 {Angstrom} thick Si{sub 3}N{sub 4} over Au-based ohmic and W gate metallizations. Due to etch selectivity, of the SF{sub 6}/0{sub 2} reactive ion etch (RIIE) generated plasma, the ohmic metal acts as an etch stop whereas the W-based refractory gate continues to etch. For etch times beyond endpoint in the range of 20 to 50%, the AFM measured via etch depth differences is 250 to 400 {Angstrom} when comparing via depths over ohmic metal and W gate metal. This etch depth difference is a specific marker for etch completion and it is measured nondestructively at a point in the process where rework is still a feasible option.
Date: December 31, 1994
Creator: Howard, A.J.; Baca, A.G. & Shul, R.J.
Partner: UNT Libraries Government Documents Department

Origin of the Time-Dependence of Wet Oxidation of AlGaAs

Description: The time-dependence of the wet oxidation of high-Al-content AlGaAs can be either linear, indicating reaction-rate limitation, or parabolic, indicating diffusion-limited rates. The transition from linear to parabolic time dependence can be explained by the increased rate of the formation of intermediate As{sub 2}O{sub 3} vs. its reduction to elemental As. A steadily increasing thickness of the As{sub 2}O{sub 3}-containing region at the oxidation front will shift the process from the linear to the parabolic regime. This shift from reaction-rate-limited (linear) to diffusion-limited (parabolic) time dependence is favored by increasing temperature or increasing Al mole fraction.
Date: February 15, 1999
Creator: Allerman, A.A.; Ashby, C.I.H.; Bridges, M.M.; Hammons, B.E. & Hou, H.Q.
Partner: UNT Libraries Government Documents Department

ICP etching of GaAs via hole contacts

Description: Deep etching of GaAs is a critical process step required for many device applications including fabrication of through-substrate via holes for monolithic microwave integrated circuits (MMICs). Use of high-density plasmas, including inductively coupled plasmas (ICP), offers an alternative approach to etching vias as compared to more conventional parallel plate reactive ion etch systems. This paper reports ICP etching of GaAs vias at etch rates of about 5.3 {mu}m/min with via profiles ranging from highly anistropic to conical.
Date: September 1, 1996
Creator: Shul, R.J.; Baca, A.G.; Briggs, R.D.; McClellan, G.B.; Pearton, S.J. & Constantine, C.
Partner: UNT Libraries Government Documents Department

Formation and properties of porous GaAs

Description: Porous structures on n-type GaAs (100) can be grown electrochemically in chloride-containing solutions. Crystallographic etching of the sample is a precursor stage of the attack. Polarization curves reveal the existanece of a critical onset potential for por formation (PFP). PFP is strongly dependent on the doping level of the sample and presence of surface defects. Good agreement between PFP and breakdown voltage of the space charge layer is found. Surface analysis by EDX, AES, and XPS show that the porous structure consists mainly of GaAs and that anion uptake in the structure can only observed after attackhas been initiated. Photoluminescence measurements reveal (under certain conditions) visible light emission from the porous structure.
Date: June 1, 1996
Creator: Schmuki, P.; Lockwood, D.J.; Fraser, J.W.; Graham, M.J. & Isaacs, H.S.
Partner: UNT Libraries Government Documents Department

Development of a GaAs Monolithic Surface Acoustic Wave Integrated Circuit

Description: An oscillator technology using surface acoustic wave delay lines integrated with GaAs MESFET electronics has been developed for GaAs-based integrated microsensor applications. The oscillator consists of a two-port SAW delay line in a feedback loop with a four-stage GaAs MESFET amplifier. Oscillators with frequencies of 470, 350, and 200 MHz have been designed and fabricated. These oscillators are also promising for other RF applications.
Date: March 8, 1999
Creator: Baca, A.G.; Casalnuovo, S.C.; Drummond, T.J.; Frye, G.C.; Heller, E.J.; Hietala, V.M. et al.
Partner: UNT Libraries Government Documents Department

Direct sublattice imaging of interface dislocation structures in CdTe/GaAs(001)

Description: This paper presents directly interpretable atomic resolution images of dislocation structures at interfaces in CdTe/GaAs(001) systems. This is achieved using the technique of Z-contrast imaging in a 300 kV scanning transmission electron microscope in conjunction with maximum entropy image analysis. In addition to being used to further the understanding of the relation between growth conditions and exhibited properties, the data presented provides direct information on the atomic arrangements at dislocation cores.
Date: January 1995
Creator: McGibbon, A.J.; Pennycook, S.J.; Angelo, J.E. & Mills, M.J.
Partner: UNT Libraries Government Documents Department

Fabrication issues of oxide-confined VCSELs

Description: To insert high-performance oxide-confined vertical-cavity surface- emitting lasers (VCSELs) into the manufacturing arena, we have examined the critical parameters that must be controlled to establish a repeatable and uniform wet thermal oxidation process for AlGaAs. These parameters include the AlAs mole fraction, sample temperature, carrier gas flow, and bubbler water temperature. Knowledge of these parameters has enable the compilation of oxidation rate data for AlGaAs which exhibits an Arrhenius rate dependence. The compositionally dependent activation energies for Al{sub x}Ga{sub 1-x}As layers of x=1.00, 0.98, and 0.92 are found to be 1.24, 1.75, and 1.88 eV, respectively. 7 figs, 1 tab, 14 refs.
Date: April 1, 1997
Creator: Geib, K.M.; Choquette, K.D.; Hou, H.Q. & Hammons, B.E.
Partner: UNT Libraries Government Documents Department

Low resistivity ohmic contacts to moderately doped n-GaAs with low temperature processing

Description: A low-temperature process for forming ohmic contacts to moderately doped GaAs has been optimized using a PdGe metallization scheme. Minimum specific contact resistivity of 1.5 {times} 10{sup {minus}6} {minus}cm{sup 2} has been obtained with a low anneal temperature of 250 C. Results for optimizing both time and temperature are reported and compared to GeAu n-GaAs contacts. Material compositions was analyzed by x-ray photoelectron spectroscopy and circuit metal interconnect contact resisitivity to the low-temperature processed PdGe contacts is reported. For the lowest temperature anneals considered, excess Ge on the ohmic contact layer is suspected of degrading interconnect metal contacts, while higher temperature anneals permitted interconnect metal formation with negligible contact resistivity. Atomic force microscopy measurements showed that the PdGe surface morphology is much more uniform than standard GeAu contacts.
Date: December 31, 1994
Creator: Lovejoy, M.L.; Howard, A.J.; Zavadil, K.R.; Rieger, D.J.; Shul, R.J. & Barnes, P.A.
Partner: UNT Libraries Government Documents Department

A polarized photoluminescence study of strained layer GaAs photocathodes

Description: Photoluminescence measurements have been made on a set of epitaxially grown strained GaAs photocathode structures. The photocathodes are designed to exhibit a strain-induced enhancement of the electron spin polarization obtainable by optical pumping with circularly polarized radiation of near band gap energy. For the case of non-strained GaAs, the degree of spin polarization is limited to 50% by crystal symmetry. Under an appropriate uniaxial compression or tension, however, the valence band structure near the gap minimum is modified such that a spin polarization of 100% is theoretically possible. A total of nine samples with biaxial compressive strains ranging from zero to {approximately}0.8% are studied. X-ray diffraction analysis, utilizing Bragg reflections, is used to determine the crystal lattice structure of the samples. Luminescence spectra and luminescence circular polarization data are obtained at room temperature, {approx}78 K and {approx}12 K. The degree of luminescence circular polarization is used as a relative measure of the photo-excited electron spin polarization. The room temperature luminescence circular polarization data is compared with the measured electron spin polarization when the samples are used as electron photo-emitters with a negative electron affinity surface preparation. The luminescence data is also analyzed in conjunction with the crystal structure data with the goal of understanding the strain dependent valence band structure, optical pumping characteristics and spin depolarization mechanisms of the photocathode structures. A simple model is used to describe the luminescence data, obtained for the set of samples. Within the assumptions of the model, the deformation potentials a, b and d for GaAs are determined. The measured values are a = -10.16{+-}.21 eV, b = -2.00{+-}.05 eV and d = -4.87{+-}.29 eV. Good agreement with published values of the deformation potentials provides support for the model used to describe the data.
Date: July 1, 1996
Creator: Mair, R.A.
Partner: UNT Libraries Government Documents Department

Composite fermions in 2 x 10{sup 6} cm{sup 2}/Vs mobility A1GaAs/GaAs heterostructures grown by MOCVD

Description: Recent growth by MOCVD (metalorganic chemical vapor deposition) of 2.0x10{sup 6} cm{sup 2}/Vs mobility heterostructures are reported. These mobilities, the highest reported to date, are attributed to use of tertiarybutylarsine as the arsenic precursor. Measurements in tilted magnetic fields of the fractional quantum Hall effect states near filling factor 3/2 are consistent with a spin-split composite fermion (CF) model proposed earlier. Extracted values of the product of the CF g-factor and CF effective mass agree with values previously obtained for MBE samples.
Date: December 31, 1996
Creator: Simmons, J.A., Chui, H.C., Harff, N.E., Hammons, B.E. & Du, R.R., Zudov, M.A.
Partner: UNT Libraries Government Documents Department