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In the present investigation, a comprehensive photonic characterization and analysis of low energy Ar⁺ ion beam processed GaAs surfaces is presented. The purpose of this investigation was to evaluate the damage and amorphization introduced at the surface and sub-surface regions by ion bombardment. Ar⁺ ion beam etching was selected in order to rule out the possibility of producing any additional effects at the interface due to chemical reactions in the case of reactive ion etching. After a brief review of the concepts and underlying physics, several photonic structures are introduced. The basic theory governing the photovoltaic devices and photoconductive samples is discussed. The preparation and characterization techniques of ion beam processed GaAs samples are described. An automated photovoltaic materials and devices (PVMD) system was developed. Asyst, a Forth based scientific software was selected to write the source codes for data acquisition and reduction. The inherent fast execution times of the software allows data acquisition in real time, ensuring the quasi-steady state condition. The electrical and optical evaluation procedures developed and employed for the present investigation are discussed. One of the striking features of the ion beam bombardment on semi-insulating (SI) GaAs samples was the observation of persistent photoconductivity. A phenomenological model for optically generated ion beam induced metastable defect state formation was proposed to explain the persistent photoconductivity. Presence of two or more exponential curves in the relaxation mode indicates the distributed nature of the traps within the band gap. A conjectural flat-band energy diagram was introduced to elucidate the proposed model. The observed dark and photoconductivity response model was based on the distributed lumped electrical components analysis. Fundamental transport equations were employed in the analysis of the lumped electrical components model. Metal-Insulator-Semiconductor (MIS) type Schottky barrier diodes and photodiodes were fabricated employing both thermal and anodic oxides. Diode parameters were evaluated as a function of ion-beam energy. An increase in reverse saturation current density accompanied by an increase in the ideality factor was observed, indicating the presence of trap-assisted tunneling and a region of high recombination. The effective barrier height was generally lowered; however, no monotonic correlation with the ion energy was observed. It is proposed that the mechanisms described in previous studies (e.g. tunneling, stoichiometry effects, ion penetration depth) were dominated by the effect of Fermi level pinning at the electronic states of process-induced defects. Deep level transient spectroscopy (DLTS) indicated the presence of at least two distinct deep trap levels, at 0.32 eV and at 0.52 eV below the conduction band edge, as a consequence of ion beam etching. The EL2 peak was evident in the virgin sample and vanished in the ion beam etched samples and such observation is in agreement with our proposed model. The photovoltaic response was characterized using illuminated current-voltage (I-V) and spectral response measurements. The ratio of external quantum efficiencies of IBE devices to unetched device indicates the regions and relative extent of the damage. Since the damage has a impact on the band-bending due to excess carrier generation, the sub-bandgap photon absorption response reveals the degree of disorder. XPS results indicated an increased surface sensitivity and change in Ga/As ratio as a function of ion beam energy. The modelling of ion-beam-processed samples was considered and several computer programs which simulate their operation are described. The depth of amorphization was calculated using the Lindhard-Scharff-SchiΦtt (LSS) theory and the standard projected range and straggle parameters, and experimental parameters. A large difference was observed in the values calculated using LSS theory and experimentally measured values, using optical probes. The difference was explained in light of the Collision-Cascade model. / Ph. D.

An electrical analysis was done on A1 and Au Schottky diodes fabricated on n-type (100) GaAs which had been bombarded with low energy Ar ions. The purpose of this study was to quantify electrically damage caused by the Ion Beam Etching (IBE) as functions of energy and fluence. Electrical studies included Deep Level Transient Spectroscopy (DLTS), Current-Voltage (I-V), Capacitance-Voltage (C-V), ConductanceVoltage (G-V), Capacitance-Temperature (C-T), and Activation Energy Analysis. These electrical measurements were carried out on GaAs which had been exposed to a variety of treatments after IBE (such as chemical etch removal) to determine damage depth. At the lowest energy studied, 0.5keV, Schottky reverse saturation currents (I_sat) increased by over 4 orders of magnitude from the virgin case. The ideality factor, n, increased slightly while the breakdown voltage decreased. The most prominent changes occurred in the DLTS spectrum where it was observed that the native arsenic defect EL2 peak disappeared completely after ion etching. Concurrently a sharp increase in the diode conductivity with temperature was seen. It was found that chemical removal of 100Å of GaAs by chemical means could restore most of the diode parameters and the EL2 peak. It is proposed that the loss of EL2 is not related to a true physical reduction (i.e. an arsenic depletion) since calculations showed that the As loss would have extended beyond 3000Å for detectable DLTS changes. Also, the EL2 peak could be made to artificially disappear on a virgin sample with an external diode shunting resistor. The loss of the EL2 peak is, rather, attributed to a thin low resistivity surface layer having a partly amorphous nonstoichiometric crystal structure which can desensitize or mask the DLTS measurement. Surface chemical etch studies over the top of the Schottky diodes recovered 25% of the EL2 peak supporting this conclusion. Lower fluences had no effect at 0.5keV. Increasing ion bombardment energy showed a steady degradation in diode ideality factors. The reverse breakdown voltage increased past the unetched value and the DLTS spectrum began to show a very slight return of EL2. At 3keV the ideality factor was large, indicating the presence of a somewhat thicker high resistance layer. In fact recovery of diode parameters and EL2 did not occur until after 100Å removal. This was much deeper than expected at this energy, according to theory. Physical and lumped R-C electrical models are reported with an accompanying computer simulation of experimental DLTS results. The simulation used both thin low resistance and thick high resistance top layers to show that EL2 could be removed artificially. The models were also somewhat successful in explaining previously reported capacitance dispersion found in IBE GaAs. / Ph. D.

The fundamental components for processing all-optically represented data, namely optical switches and logic gates are investigated. Improved techniques for fabricating nonlinear Fabry-Perot etalons containing GaAs have brought a proliferation of GaAs optical bistable devices. These devices show significant improvements in speed, power requirements, operating temperature and thermal stability. Experiments verify predictions that one can operate a single nonlinear etalon as optical logic gates or two such etalons as a flip-flop. Optimization of the logic gates is then discussed from a systems approach.

Call number: LD2668 .T4 1986 Y36 / Master of Science / Physics

by Chan Lai Yin Simon. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references. / Chapter Chapter 1: --- Introduction / Chapter 1.1 --- Background --- p.1-2 / Chapter 1.2 --- Properties of the InGaAsP quaternary alloy on InP substrate --- p.2 / Chapter 1.2.1 --- Physical Properties of In1-xGaxASyP1-y on InP substrate --- p.3-4 / Chapter 1.2.2 --- Optical Properties of In1-xGaxASyP1-y on InP substrate --- p.4-7 / Chapter 1.2.3 --- Nonlinear Optical Property of InGaAsP --- p.7-9 / Chapter 1.3 --- Fabrication of InGaAsP/InP rib waveguide / Chapter 1.3.1 --- Epitaxial Growth of In1-xGaxASyP1-y on InP substrate by MOCVD --- p.9 / Chapter 1.3.2 --- Etching of the five layer In1-xGaxASyP1-y slab waveguide --- p.9-12 / Chapter 1.4 --- Overview of the thesis --- p.12-13 / References --- p.13-15 / Chapter Chapter 2: --- Modal analysis of the single mode III-V semiconductor waveguidesin multi-layer rib structure by Effective Index Method / Chapter 2.1 --- Introduction --- p.16-17 / Chapter 2.2 --- Modal analysis of the rib waveguides --- p.17-27 / Chapter 2.3 --- Optical Confinement in rib waveguide --- p.28-30 / Chapter 2.4 --- Conclusions and discussions --- p.30-31 / References --- p.31-33 / Chapter Chapter 3: --- Ultrashort Pulsewidth Measurement Part I / Chapter 3.1 --- Introduction --- p.34 / Chapter 3.2 --- Pulsewidth measurement by streak camera --- p.34-37 / Chapter 3.3 --- Pulsewidth measurement by nonlinear autocorrelation --- p.37-40 / Chapter 3.3.1 --- Second Harmonic Generation Autocorrelator --- p.40-43 / Chapter 3.3.2 --- Two Photon Fluorescence Autocorrelator --- p.43-44 / Chapter 3.4 --- Two Photon Absorption Waveguide Autocorrelator --- p.45 / Chapter 3.4.1 --- TPA theory --- p.45-48 / Chapter 3.4.2 --- Autocorrelation Measurement by TPA in InGaAsP Waveguide --- p.48-51 / Chapter 3.4.3 --- The Estimated performance of the TPA Waveguide Autocorrelator --- p.52 / References --- p.52-57 / Chapter Chapter 4: --- Ultrashort Pulsewidth Measurement Part II: High Sensitivity Two Photon Absorption InGaAsP Waveguide Autocorrelator for Low Power Pulsewidth Measurement of 1.55μm Waveguide Pulses / Chapter 4.1 --- Introduction --- p.58-60 / Chapter 4.2 --- Waveguide structures --- p.60 / Chapter 4.3 --- Practical Implementation of the TPA Waveguide Autocorrelator / Chapter 4.3.1 --- Mirror arrangement for the delay system --- p.61 -63 / Chapter 4.3.2 --- Alignment and Coupling of the InGaAsP/InP Waveguide --- p.63-64 / Chapter 4.3.3 --- TPA photocurrent detection --- p.64-65 / Chapter 4.4 --- Experimental results --- p.65-67 / Chapter 4.4.1 --- Pulsewidth measurement of the TPA InGaAsP waveguide autocorrelator --- p.67-71 / Chapter 4.4.2 --- Spectral analysis by the TPA InGaAsP waveguide autocorrelator --- p.71 -73 / Chapter 4.5 --- Conclusions and discussions --- p.73-75 / References --- p.75-78 / Chapter Chapter 5: --- Picosecond Pulses Generation by Colliding-Pulse Mode-locking of a Fabry-Perot Laser Diode with an Intra-cavity Gradual Degradation Defect / Chapter 5.1 --- Introduction --- p.79-80 / Chapter 5.2 --- Gain-switching --- p.80-84 / Chapter 5.3 --- Colliding Pulse Mode-locking --- p.84-85 / Chapter 5.3.1 --- Degradation of diode laser --- p.85-86 / Chapter 5.3.2 --- CPM Theory --- p.86-89 / Chapter 5.3.3 --- Experimental results --- p.89-92 / Chapter 5.4 --- Conclusions and discussions --- p.92-93 / References --- p.94-98 / Chapter Chapter 6: --- Conclusions / Chapter 6.1 --- Summary of the Research / Chapter 6.1.1 --- Theoretical Results --- p.99-100 / Chapter 6.1.2 --- Experimental Results --- p.101-104 / Chapter 6.2 --- Future Development / Chapter 6.2.1 --- Improvement of the TPA InGaAsP waveguide autocorrelator --- p.105 / Chapter 6.2.2 --- Future development of III-V semiconductor waveguides --- p.105-107 / References --- p.107-108 / Appendix --- p.109-121

by So King Lung, Benny. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves 102-109). / ABSTRACT --- p.v / ACKNOWLEDGEMENTS --- p.vii / LIST OF FIGURES --- p.viii / LIST OF TABLES --- p.xiii / Chapter Chapter 1 --- Background of the study --- p.1 / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- Surface passivation techniques --- p.3 / Chapter 1.2.1 --- Sulfide solution passivation --- p.3 / Chapter 1.2.2 --- Gas-phase sulfide passivation --- p.4 / Chapter 1.3 --- Surface structure of sulfide-passivated surface --- p.5 / Chapter 1.4 --- Objectives of the present study --- p.7 / Chapter Chapter 2 --- Instrumentation --- p.9 / Chapter 2.1 --- Introduction --- p.9 / Chapter 2.2 --- X-ray photoelectron spectroscopy (XPS) --- p.9 / Chapter 2.2.1 --- The development of XPS --- p.9 / Chapter 2.2.2 --- Basic principle of XPS --- p.9 / Chapter 2.2.3 --- Quantitative analysis of XPS --- p.14 / Chapter 2.2.3.1 --- Atomic concentration of a homogenous material --- p.14 / Chapter 2.2.3.2 --- Layer structure --- p.15 / Chapter 2.2.3.3 --- Simulation of XPS atomic concentration ratios from proposed surface structural models --- p.17 / Chapter 2.2.4 --- XPS experiment --- p.19 / Chapter 2.3 --- Low energy electron diffraction (LEED) --- p.21 / Chapter 2.3.1 --- The development of LEED --- p.21 / Chapter 2.3.2 --- Basic principle of LEED --- p.23 / Chapter 2.3.3 --- LEED experiment --- p.28 / Chapter 2.3.3.1 --- The ultra high vacuum chamber (UHV) --- p.28 / Chapter 2.3.3.2 --- The electron gun --- p.28 / Chapter 2.3.3.3 --- The sample --- p.30 / Chapter 2.3.3.4 --- The detector system --- p.30 / Chapter Chapter 3 --- Surface treatments --- p.31 / Chapter 3.1 --- Semiconductor wafers --- p.31 / Chapter 3.2 --- Cleaning procedure --- p.31 / Chapter 3.3 --- Polysulfide passivation --- p.33 / Chapter Chapter 4 --- Gas-phase polysulfide passivation of the InP(100) surface --- p.37 / Chapter 4.1 --- Introduction --- p.37 / Chapter 4.2 --- Sulfide-assisted reordering at the InP(100) surface --- p.38 / Chapter 4.2.1 --- Gas-phase polysulfide-treated InP( 100) surface --- p.38 / Chapter 4.2.2 --- Further annealing of the gas-phase polysulfide-treated surface --- p.47 / Chapter 4.2.3 --- Comparison with the UV/O3-HF treatment --- p.48 / Chapter 4.2.4 --- Sulfide at the interface of SiNx/InP --- p.49 / Chapter 4.3 --- Conclusions --- p.53 / Chapter Chapter 5 --- Gas-phase polysulfide passivation of the GaAs(lOO) surface --- p.55 / Chapter 5.1 --- Introduction --- p.55 / Chapter 5.2 --- Gas-phase poly sulfide-passivated GaAs( 100) surface --- p.56 / Chapter 5.2.1 --- Surface structure of the as-treated surface --- p.56 / Chapter 5.2.2 --- Surface structure after further annealing --- p.64 / Chapter 5.2.3 --- Mechanism of the gas-phase polysulfide passivation --- p.67 / Chapter 5.3 --- Conclusions --- p.68 / Chapter Chapter 6 --- Gas-phase polysulfide passivation of the GaAs(100) surface --- p.69 / Chapter 6.1 --- Introduction --- p.69 / Chapter 6.2 --- Reordering at the gas-phase polysulfide-passivated GaAs(100) surface --- p.70 / Chapter 6.2.1 --- Adsorption of polysulfide on the GaAs(100) surface --- p.70 / Chapter 6.2.2 --- Ordered sulfide at the GaAs(l 10) surface --- p.73 / Chapter 6.2.3 --- Further analysis of the LEED pattern --- p.80 / Chapter 6.3 --- Conclusions --- p.83 / Chapter Chapter 7 --- Sulfide Solution passivation of the GaAs(100) surface --- p.84 / Chapter 7.1 --- Introduction --- p.84 / Chapter 7.2 --- Sulfide solution passivation on the GaAs(l 10) surface --- p.85 / Chapter 7.2.1 --- Etching of sulfide solution on the GaAs(l 10) surface --- p.85 / Chapter 7.2.2 --- Annealing of sulfide solution-passivated GaAs( 110) surface --- p.88 / Chapter 7.2.3 --- Further analysis of the LEED pattern --- p.92 / Chapter 7.2.4 --- Shift of XPS peak position during annealing --- p.95 / Chapter 7.3 --- Conclusions --- p.97 / Chapter Chapter 8 --- Conclusions and further work --- p.99 / Chapter 8.1 --- Conclusions --- p.99 / Chapter 8.2 --- Further work --- p.100 / References --- p.102

by Lam Siu Dan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (leaves 65-67). / Text in English; abstracts in English and Chinese. / by Lam Siu Dan. / Table of contents --- p.I / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Interest in GaAs1-xNx/GaAs alloy --- p.1 / Chapter 1.2 --- Interest in growing GaAs1-xNx/GaAs using different carrier gases --- p.4 / Chapter 1.3 --- Theoretical calculation of the band gap energy of GaAs1-xNx alloy --- p.4 / Chapter 1.4 --- Advantages of using photoluminescence (PL) --- p.7 / Chapter 1.5 --- Our work --- p.9 / Chapter Chapter 2 --- Experimental setup and procedures / Chapter 2.1 --- Growth conditions of GaAs1-xNx on (001) GaAs --- p.10 / Chapter 2.2 --- X-ray diffraction / Chapter 2.2.1 --- Setup --- p.12 / Chapter 2.2.2 --- Types of X-ray measurements --- p.12 / Chapter 2.3 --- PL measurements / Chapter 2.3.1 --- Setup --- p.14 / Chapter 2.3.2 --- Types of PL measurement --- p.16 / Chapter Chapter 3 --- Results and discussions / Chapter 3.1 --- X-ray diffraction of GaAs1-xNx/GaAs / Chapter 3.1.1 --- GaAs1-xNx/GaAs grown using H2 as carrier gas --- p.17 / Chapter 3.1.2 --- GaAs1-xNx/GaAs grown using N2 as carrier gas --- p.28 / Chapter 3.1.3 --- Peak widths of the X-ray rocking curves of GaAs1-xNx/GaAs --- p.30 / Chapter 3.2 --- Room temperature (RT) and 10K PL of GaAs1-xNx/GaAs / Chapter 3.2.1 --- The energy of the NBE peak of GaAs1-xNx/GaAs --- p.32 / Chapter 3.2.2 --- The width of the NBE peak of GaAs1-xNx/GaAs --- p.44 / Chapter 3.3 --- Excitation power density (EPD) dependent PL studies of GaAs1-xNx/GaAs / Chapter 3.3.1 --- The energy of the NBE peak of GaAs1-xNx/GaAs --- p.49 / Chapter 3.3.2 --- The width of the NBE peak of GaAs1-xNx/GaAs --- p.55 / Chapter 3.4 --- Temperature dependent PL studies of GaAs1-xNx/GaAs --- p.57 / Chapter Chapter 4 --- Conclusions --- p.62 / References --- p.63

Graduation date: 1993

The low thermal conductivity of gallium arsenide compared to silicon results in self-heating effects in GaAs MESFETs that limit the electrical performance of such devices for high power applications. To date, analytical thermal models of self heating in GaAs MESFETs are based on the assumption of a uniformly heated channel. This thesis presents a two dimensional analysis of the electrothermal effect of this device based on the two dimensional power density distribution in the channel under various bias conditions. The numerical simulation is performed using the finite difference technique. The results of the simulation of an isothermal MESFET without heat effects is compared with various one dimensional analytical models in the literature. Electro thermal effects into the two-dimensional isothermal MESFET model allowed close examination of the temperature profile within the MESFET. The large gradient in power distribution results in a localized heat source within the channel which increases the overall channel temperature, which shows that the assumption of a uniformly heated channel is erroneous, and may lead to an underestimation of the maximum channel temperature. / Graduation date: 1992