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Articles 781 - 799 of 799

Full-Text Articles in Semiconductor and Optical Materials

A Novel Technique For Deep Level Characterization Of High-Resistivity Semiconductor Materials, Sridhar Panigrahi Jul 1992

A Novel Technique For Deep Level Characterization Of High-Resistivity Semiconductor Materials, Sridhar Panigrahi

Electrical & Computer Engineering Theses & Dissertations

An improved photo induced current transient spectroscopy (PICTS) technique is developed for studying deep level parameters in high-resistivity semiconductor materials. A new digital data acquisition approach and improvement in the cryogenics of the system have enabled us, for the first time in our laboratory, to detect CuA level in a copper doped silicon compensated gallium arsenide (GaAs:Si:Cu) sample. The digital approach improves both the signal to noise ratio (S/N) and the efficiency of the system. Also, multiple PICTS spectra in a single thermal cycle can be obtained. In the present work, various doped and undoped gallium arsenide ( GaAs) and …

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A Response Surface Methodology Study Of Ferroelectric Memory Devices, Kevin C. Smith Mar 1992

A Response Surface Methodology Study Of Ferroelectric Memory Devices, Kevin C. Smith

Theses and Dissertations

Fatigue in ferroelectric memory devices was studied. The application of fatigue pulses to a ferroelectric sample was controlled by the RT-66 Ferroelectric Tester, a variation of the Sawyer-Tower circuit. The RT-66 also controlled data collection following the fatiguing process. Seven variables were evaluated for their potential- affect on fatigue. A sequence of fatigue tests, which varied the settings of these variables, was developed using Response Surface Methodology (RSM) experimental designs. Least-squares regression models were developed once a particular RSM set of design experiments was completed. These models were evaluated using RSM tools, and the analysis of these models allowed the …

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Application Of Stable Operating Criterion To Grating Tuned Strong External Feedback Semiconductor Lasers, Haiyin Sun, Malay K. Mazumder Jan 1992

Application Of Stable Operating Criterion To Grating Tuned Strong External Feedback Semiconductor Lasers, Haiyin Sun, Malay K. Mazumder

Journal of the Arkansas Academy of Science

Stability analysis is done by applying criterion dnQ((o)/cfco>0 for grating tuned strong external feedback semiconductor lasers. The resulting stable and unstable operating ranges agree well with experiment results.

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Techniques For Efficiency Calibration Of Photon Detectors For X-Rays And Low Energy Gamma Rays, Rahul Mehta Jan 1992

Techniques For Efficiency Calibration Of Photon Detectors For X-Rays And Low Energy Gamma Rays, Rahul Mehta

Journal of the Arkansas Academy of Science

No abstract provided.

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Characterizing The Sensitivity, Selectivity, And Reversibility Of The Metal-Doped Phthalocyanine Thin-Films Used With The Interdigitated Gate Electrode Field-Effect Transistor (Igefet) To Detect Organophosphorous Compounds And Nitrogen Dioxide, Clayton P. Howe Dec 1991

Characterizing The Sensitivity, Selectivity, And Reversibility Of The Metal-Doped Phthalocyanine Thin-Films Used With The Interdigitated Gate Electrode Field-Effect Transistor (Igefet) To Detect Organophosphorous Compounds And Nitrogen Dioxide, Clayton P. Howe

Theses and Dissertations

This study investigated the sensitivity, reversibility, and selectivity of the thin film coatings used on the interdigitated gate electrode field effect transistor (IGEFET) gas microsensor. These responses were quantified based on the dc resistance changes and frequency domain responses of the microsensor. The thin-film materials included: copper phthalocyanine (CuPc), nickel phthalocyanine (NiPc), and cobalt phthalocyanine (CoPc). The challenge gases included: diisopropyl methylphosphonate (DIMP), dimethyl methylphosphonate (DMMP), nitrogen dioxide, ammonia, and boron trifluoride. Tests of the CuPc thin-films and nitrogen dioxide challenges established the primary set of test parameters expected to maximize the selectivity, sensitivity, and reversibility of the thin-film coatings. …

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Cathodoluminescence Of Gaas, Tyler Smith Jul 1991

Cathodoluminescence Of Gaas, Tyler Smith

Electrical & Computer Engineering Theses & Dissertations

Cathodoluminescence of band-gap radiation across the bulk of a proposed semiconductor switch has been studied. Such a device relies on the efficient use of cathodoluminescence to modulate the conductivity of the switch. Diagnostics were configured to measure the intensity of band-gap radiation across the bulk of several switch samples. The measured results were compared to calculations based on a four energy level band-gap model which included two deep levels EL2 and HL10.

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Monte Carlo Simulation Of Millimeter-Wave Gunn Effect Oscillators, Ramani Vaidyanathan Apr 1991

Monte Carlo Simulation Of Millimeter-Wave Gunn Effect Oscillators, Ramani Vaidyanathan

Electrical & Computer Engineering Theses & Dissertations

Monte Carlo simulations have been carried out to investigate the performance of microwave Gunn oscillators. Three separate aspects of the simulation problem have been comprehensively addressed in this work. First, the presence of an external circuit has been self-consistently incorporated into the calculations. The inclusion of the external circuit facilitates a study of the circuit controlled regime, and correctly models effects arising from the time dependent boundary conditions. Secondly, microscopic details of the electronic relaxation mechanisms which ultimately control the frequency response limits, have been taken into account through an iterative Monte Carlo-Poisson scheme. This procedure overcomes a potential shortcoming …

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Q Improvement Of A 5.2 Ghz Te011 Cavity By Incorporating Y1Ba2Cu3O7-X, R. Joseph Leclear Apr 1991

Q Improvement Of A 5.2 Ghz Te011 Cavity By Incorporating Y1Ba2Cu3O7-X, R. Joseph Leclear

Electrical & Computer Engineering Theses & Dissertations

Research is undertaken to apply high temperature superconducting material to improve the quality factor (Q) of a 5.2 GHz cylindrical resonant cavity. In particular, the approach is to electrophoretically deposit polycrystalline Y1Ba2Cu3O7-x (YBCO) on the conducting surface of the cavity cylinder. Spalling of the YBCO ceramic coating due to expansion and contraction of the cavity during sintering and testing is overcome by segmenting the cylinder. Results show that the Q of the cavity is increased over that of a copper cavity at temperatures below 60 K. At 20 K, improvement exceeds a factor …

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Fluorescent Lifetime Measurements Of Rare Earth Elements In Gallium Arsenide, Danny J. Topp Dec 1990

Fluorescent Lifetime Measurements Of Rare Earth Elements In Gallium Arsenide, Danny J. Topp

Theses and Dissertations

Lifetime measurements of the excited states of three GaAs semiconductors doped with the rare earth elements Erbium (ER), Praseodymium (Pr) , and Thulium (Tm) has been studied using a pulsed nitrogen laser and germanium detector. The measurements were made with an experimental set up with a system response time of 0.34 micro seconds. A 330 milliwatt nitrogen laser with a wavelength of 3370 angstrums was used to excite transitions of the rare earth elements.

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Angle Of Arrival Detection Through Artificial Neural Network Analysis Of Optical Fiber Intensity Patterns, Scott Thomas Dec 1990

Angle Of Arrival Detection Through Artificial Neural Network Analysis Of Optical Fiber Intensity Patterns, Scott Thomas

Theses and Dissertations

The optical sensors of United States Air Force reconnaissance vehicles, such as satellites, are subject to temporary or permanent blinding from hostile (or threat) laser radiation. By detecting and determining the angle of arrival (AOA) of the hostile radiation, the reconnaissance vehicle may be able to protect its optical sensors by taking evasive maneuvers or by shutting down the optical sensor (such as closing a shutter) until the threat has passed. In addition, the vehicle can relay information to its ground terminal allowing the intelligence community to determine the source of the hostile laser radiation. This thesis demonstrated that an …

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Low Temperature Photoluminescence Study Of Holmium And Thulium Implanted Into Iii-V Semiconductors And Silicon, Eric Silkowski Dec 1990

Low Temperature Photoluminescence Study Of Holmium And Thulium Implanted Into Iii-V Semiconductors And Silicon, Eric Silkowski

Theses and Dissertations

Low temperature photoluminescence studies were performed on holmium implanted into InP, GaAs, and Si; and thulium implanted into AlGaAs, GaAs, and Si. Samples were annealed by the conventional furnace and rapid thermal techniques. None of the characteristic 4f emissions of holmium were found in the spectral region of .73 to 1.55 eV. AlGaAs:Tm showed strong thulium emissions in the .93 to 1.03 eV region. These emissions were studied and compared to those in GaAs:Tm. Low and high temperature annealed samples showed evidence of trivalent Tm centers. Temperature dependence studies showed that thulium 4f emissions were present above 200 K but …

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Characterization Of Barium Titanate As An Optical Amplifier, George A. Vogel Dec 1990

Characterization Of Barium Titanate As An Optical Amplifier, George A. Vogel

Theses and Dissertations

The introduction of two-beam coupling in photorefractive materials has resulted in an extensive amount of research into their use as optical processing/computing elements. This dissertation develops the theoretical equations for two-beam coupling in barium titanate as an optical amplifier. One of the factors which limits the optical gain in photorefractive crystals is the loss of pump beam power to the amplification of parasitic light (beam fanning). This parasitic light is produced by light scattered from the pump beam by imperfections on both the crystal face and within the crystal. Through the analysis of signal and noise amplification as functions of …

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Optical And High Electric Field Effects In Bulk Gallium Arsenide Switches, Randy Roush Oct 1990

Optical And High Electric Field Effects In Bulk Gallium Arsenide Switches, Randy Roush

Electrical & Computer Engineering Theses & Dissertations

During the past few years, bulk, photoconductive switching has become recognized as a viable topic for future research on moderate and high power switches. The two-pulse, or BOSS, concept relies on an excitation laser pulse, and a separate de-excitation pulse in conjunction with silicon doped, copper compensated, GaAs to create a variable temporal electrical pulse width. The research contained in this document provides information concerning the feasibility of the BOSS concept, as the switch is scaled to larger sizes, and higher voltage and current. The major concern will be the high voltage and current effects. The absorption length for 1064 …

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Influence Of Copper Doping On The Performance Of Optically Controlled Gaas Switches, St. T. Ko, V. K. Lakdawala, K. H. Schoenbach, M. S. Mazzola Jan 1990

Influence Of Copper Doping On The Performance Of Optically Controlled Gaas Switches, St. T. Ko, V. K. Lakdawala, K. H. Schoenbach, M. S. Mazzola

Electrical & Computer Engineering Faculty Publications

The influence of the copper concentration in silicon-doped gallium arsenide on the photoionization and photoquenching of charge carriers was studied both experimentally and theoretically. The studies indicate that the compensation ratio (NCu/NSi) is an important parameter for the GaAs:Si:Cu switch systems with regard to the turn-on and turn-off performance. The optimum copper concentration for the use of GaAs:Si:Cu as an optically controlled closing and opening switch is determined.

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Gaas Photoconductive Closing Switches With High Dark Resistance And Microsecond Conductivity Decay, M. S. Mazzola, K. H. Schoenbach, V. K. Lakdawala, R. Germer, G. M. Loubriel, F. J. Zutavern Jan 1989

Gaas Photoconductive Closing Switches With High Dark Resistance And Microsecond Conductivity Decay, M. S. Mazzola, K. H. Schoenbach, V. K. Lakdawala, R. Germer, G. M. Loubriel, F. J. Zutavern

Electrical & Computer Engineering Faculty Publications

Silicon-doped n-type gallium arsenide crystals, compensated with diffused copper, were studied with respect to their application as photoconductive, high-power closing switches. The attractive features of GaAs:Cu switches are their high dark resistivity, their efficient activation with Nd:YAG laser radiation, and their microsecond conductivity decay time constant. In the authors' experiment, electric fields are high as 19 kV/cm were switched, and current densities of up to 10 kA/cm2 were conducted through a closely compensated crystal. At field strengths greater than approximately 10 kV/cm, a voltage `lock-on' effect was observed.

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Nanosecond Optical Quenching Of Photoconductivity In A Bulk Gaas Switch, M. S. Mazzola, K. H. Schoenbach, V. K. Lakdawala, S. T. Ko Jan 1989

Nanosecond Optical Quenching Of Photoconductivity In A Bulk Gaas Switch, M. S. Mazzola, K. H. Schoenbach, V. K. Lakdawala, S. T. Ko

Electrical & Computer Engineering Faculty Publications

Persistent photoconductivity in copper-compensated, silicon-doped semi-insulating gallium arsenide with a time constant as large as 30 µs has been excited by sub-band-gap laser radiation of photon energy greater than 1 eV. This photoconductivity has been quenched on a nanosecond time scale by laser radiation of photon energy less than 1 eV. The proven ability to turn the switch conductance on and off on command, and to scale the switch to high power could make this semiconductor material the basis of an optically controlled pulsed-power closing and opening switch.

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An Optically Controlled Closing And Opening Semiconductor Switch, K. H. Schoenbach, V. K. Lakdawala, R. Germer, S. T. Ko Jan 1988

An Optically Controlled Closing And Opening Semiconductor Switch, K. H. Schoenbach, V. K. Lakdawala, R. Germer, S. T. Ko

Electrical & Computer Engineering Faculty Publications

A concept for a bulk semiconductor switch is presented, where the conductivity is increased and reduced, respectively, through illumination with light of different wavelengths. The increase in conductivity is accomplished by electron ionization from deep centers and generation of bound holes. The reduction of conductivity is obtained by hole ionization from the excited centers and subsequent recombination of free electrons and holes. The transient behavior of electron and hole density in a high power semiconductor (GaAs:Cu) switch is computed by means of a rate equation model. Changes in conductivity by five orders of magnitude can be obtained.

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A Laser Hydrophone, Steven Kenneth Barnoske Jan 1977

A Laser Hydrophone, Steven Kenneth Barnoske

Retrospective Theses and Dissertations

This report proposes a novel technique for measuring of acoustic fields in water. A Laser Hydrophone is proposed taking advantage of the properties of Total Internal Reflection. A theoretical analysis of the idea is presented followed by a prediction of the operating characteristics of an actual system. Actual data were taken with the proposed system and it is compared to the predicted.

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Semi-Conducting Properties Of Gray Tin As A Laboratory Introduction To Solid State Physics, Glenn F. Powers, Gene E. Louallen, Robert M. Rickett Jan 1958

Semi-Conducting Properties Of Gray Tin As A Laboratory Introduction To Solid State Physics, Glenn F. Powers, Gene E. Louallen, Robert M. Rickett

Journal of the Arkansas Academy of Science

No abstract provided.

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