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The fabrication and optical and electrical properties of a modulation-doped multiquantum-well (MD-MQW) AlGaInP light-emitting diode (LED), grown by low-pressure metal-organic vapor-phase epitaxy (LP-MOVPE), are analyzed. The n-type MD-MQW LEDs are better than conventional undoped-MQW LEDs, which are attributed to the presence of the large number of mobile electrons in the MD-MQW structure.

Proton implantation is used for fabricating AlGaN/GaN high electron mobility transistors (HEMTs) and the breakdown voltage of these HEMTs is increased without sacrificing dc characteristics. The increase of the breakdown voltage is because of the expansion of the depletion region under the two-dimensional (2-D) electron gas (2-DEG) channel.

Advanced transmission electron microscopy is combined with high-precision first-principles calculation to examine atomic-scale structures of the LaAl[O.sub.3]/Ti[O.sub.2] interface and bridge to their electronic property at the atomic level. The electronic structure is characterized and interfacial bonding is shown to be of a mixed covalent-ionic character.

Electrical spin-injection across the [Fe.sub.3][O.sub.4]:[Al.sub.0.1][Ga.sub.0.9]As interface is measured. The studies have shown the first step in the integration of molecular beam epitaxy-grown magnetic oxides into III-V semiconductor devices.

Reflection high-energy electron diffraction is used for analyzing the growth of AlInN alloys by molecular-beam epitaxy, where in-plane lattice constant and specular beam intensity oscillations are recorded for information of lattice misfit and growth rate as a function of source flux and temperature. The dependence of alloy growth rate on indium flux is observed, which has reflected the specific incorporation kinetics of indium in the alloy.

Superconductor-normal metal-insulator-superconductor Nb/Al-Al[O.sub.x]/Nb Josephson junctions are developed with Al layer, which has resulted in nonhysteretic current-voltage characteristics for critical current densities. Stewart-McCumber parameters from 1 to 3 that is optimum for digital single-flux-quantum applications are obtained without external shunting, even though the specific capacitance is very high.

Several first-principles calculations are conducted to explain the saturation magnetization, as well as the magnetocrystalline anisotropy of the various MnAl permanent magnets. The maximum energy product of the magnet is also determined.

Electric field induced (Stark) shifts is studied in mid-infrared (IR) transitions that have occurred in type II AlSb/InAs/GaSb quantum wells. Low temperature current-voltage, capacitance-voltage and photocurrent measurements are used for characterizing a type II quantum well structure that has displayed a blueshift in the lowest energy transitions that is roughly linear with applied bias and is comparable to the potential drop across the structure.

A study was conducted to examine the mechanisms that change the critical current density ([J.sub.c]) of Nb/Al[O.sub.x]/Al/Nb Josephson junctions due to the inclusion of hydrogen in the Nb electrodes. The results revealed that the [J.sub.c] change is caused by a Nb work function increase due to the hydrogen inclusion which result in an increase in barrier height.

A study was conducted to mathematically analyze the effects of several parameters, including sample temperature, intensity of the ultraviolet (UV) light, wavelength, and intensity of the laser light on the charge status of surface states in an AlGaN/GaN heterostructure. The results obtained for the effect of the ambient illumination could be applied to achieve a higher sensitivity for an AlGaN/GaN sensor and discover their future applications.

Quantitative deuterium analysis is developed by using the neodymium doped yttrium aluminum garnet laser-induced breakdown spectroscopy (LIBS) with atmospheric pressure surrounding He gas by studying the appropriate experimental condition and special sample cleaning method. The results have shown the achievement of a full resolution between the D and H emission lines from zircaloy-4 samples and a linear calibration line with zero intercept is obtained for the emission intensity of deuterium from zircaloy samples.

The parallel arrays of superconducting Nb/Al[O.sub.x]/Nb tunnel junctions nonevenly distributed in a superconducting Nb/SiO/Nb microstrip transmission line are examined to understand the discretized Josephson transmission lines (DJTLs) and magnetic flux quanta ('fluxons') in the device which could travel as solitonic waves. The results suggested that nonuniform DJTLs could be applied as a promising type of Josephson device for submillimeter-wave oscillators and fast fluxon-based electronics.

A newly designed chemical vapor deposition (CVD) reactor is used to grow a nonpolar GaN crystal on lattice-matched [100] [gamma]-LiAl[O.sub.2] substrate. The enhanced quality of the as-grown GaN {1010} epilayer on [100] [gamma]-LiAl[O.sub.2] substrate is demonstrated by using the modified inner structure of the CVD reactor.

The composition of [beta]- precipitates in an Al-Mg-Si alloy is examined by using atom probe tomography, ab initio density functional calculations and quantitative electron diffraction. Ab initio calculations have shown that replacing the [Si.sub.3]-site by aluminum has led to energetically favorable compositions consistent with the other phases in the precipitation sequence.

The preparation of metal/interlayer/semiconductor (MIS) diodes formed by coating of an organic film to p-Si semiconductor substrate is reported. Modification of the interfacial potential barrier of Al/p-Si diode achieved by using a thin interlayer of the PSP organic material is attributed to the PSP organic interlayer which increased the effective barrier height by influencing the space-charge region of Si.

A study about the short term oxidation behavior of [gamma]-TiAl treated in low-concentration phosphoric acid solution at 900 degree [Celsius] in air is reported. The transformation of the pyrophosphate film into a Ti[O.sub.2] solid solution containing phosphorus during the initial course of oxidation at 900 degree [Celsius] is found to impede the usual oxides external growing mechanisms and leads to an internal development of the oxide scale with an associated reduced oxidation rate.

A criterion is proposed for evaluating the glass-forming ability of alloy systems. Regression analysis between the logarithm of the critical cooling rate In [R.sub.c] and [theta] has produced value of [alpha] = 0.0728 and a fine linear relationship is present between criterion [theta] and In [R.sub.c] with a coefficient of determination [R.sup.2] = 0.942.

The intrinsic high-frequency (HF) behavior of three-terminal junctions based on InGaAs/InAlAs heterostructures is examined by using a well-calibrated three-dimensional semiclassical ensemble Monte Carlo simulation model. The studies have shown the important role played by surface charge effects in the frequency regime.

Rutherford backscattering spectrometry and x-ray diffraction has shown good correlations between the [Eu.sup.2+] emission linewidth and key structural parameters of [In.sub.x][Al.sub.1-x]N films on GaN in the composition range near lattice matching. [Eu.sup.3+] emission from [In.sub.0.13][Al.sub.0.87]N:Eu has shown less thermal quenching than GaN:Eu and InAlN films are superior to GaN for rear earth (RE) optical doping.

Monte Carlo simulations were applied to study two different narrow band gap semiconductors, InAs and InSb, and their associated heterostructures, AlSb/InAs and AlInSb/InSb. The results suggested that the experimentally mobile values for the model could be correctly reproduced by optimizing the bulk simulation parameters of the heterostructures and adjusting the strength of roughness scattering.

A current-sensing atomic force microscopy is used for measuring the nanoscale capacitance spectroscopy of the two-dimensional electron gas (2DEG) of AlGaN/GaN heterostructures. The current-sensing method has detected the change in Schottky barriers of the probe-sample contact, which has affected the measurement of the threshold voltage of 2DEG.

Deep level transient spectroscopy (DLTS) measurements are used for studying GaN/AlGaN/SiC heterostructures prepared by low-pressure metalorganic vapor phase epitaxy. The energy of the deep level has decreased with increasing electrical field due to Poole-Frenkel effect and the carrier capture kinetics have shown interacting point defects arranged along a line, probably a threading dislocation.

A heterostructure with three AlGaN layers with successively increasing Ga contents and compressive strains was grown on an AlN template layer to examine the strain relaxation produced by inclined threading dislocations in AlGaN. The study evidence indicated that local strain inhomogeneities due to neighboring dislocations influenced the specific bend angles of individual dislocations in AlGaN and the lattice-mismatch strain also influenced the average bend angle.

The in-plane effective mass in the two-dimensional electron gas of nominally undoped AlGaN/GaN heterostructures with a different degree of quantum confinement is examined. The contribution of the wave-function hybridization has played the dominant role and the band edge effective mass value is deduced.

The structural properties of AlGaN/GaN heterostructures grown by metal organic chemical vapor deposition on sapphire substrate with different thicknesses are examined by using high-resolution x-ray diffraction and Raman scattering methods. The studies have shown that the increase in substrate thickness has led to a reduction in dislocation density in the layers and an increase in the elastic deformations.

High quality GaSb layers are grown on semi-insulating (001) GaAs substrates by molecular-beam epitaxy by using AlSb and GaSb buffer layers and strong photoluminescence is observed for temperatures higher than 100 K. The increase in the excitation power has shown increase in the ratio of the acceptor-bound exciton with respect to the donor-acceptor pair transition due to the saturation of the donor-acceptor pair transitions.

The effect of growth conditions on the structural and electrical properties of the AlGaN/GaN high electron mobility transistor heterostructures grown on Si(111) is examined. The effect of the dislocation density on the GaN buffer insulating properties and the two-dimensional electron gas transport properties at the [Al.sub.x][Ga.sub.1-x]N/GaN interface is analyzed.

A Q-switched neodymium doped yttrium aluminum garnet laser at a peak intensity of 2.5 GW/cm2 used to study multiphoton absorption and refraction in [Mn,sup.2+] doped ZnS quantum dots. The results showed four-photon absorption and self-defocusing nonlinear refraction in ZnS and [Mn.sup.2+] doped ZnS quantum dots of sizes 2-3 nm with 1064 nm radiation.

The effect of pre-existing random roughness on the evolution of ripple structures in [O.sub.2.sup.+] sputtered thin Al films is examined. The studies have shown that coating a flat Si surface with ultrathin Al film and subsequent removal of the Al layer by oblique [O.sub.2.sup.+] sputtering has led to the formation of ripple pattern with moderate amplitude in the Si matrix at much lower effective fluence than would be in Si without Al masking.

AlGaN/AlN/GaN high electron mobility transistor heterostructures grown by metal-organic chemical vapor deposition are studied by temperature dependent time-resolved photoluminescence. The self-consistent calculation of the band potential profile has suggested a recombination mechanism for the AlGaN-related emission involving electrons confined in the triangular AlGaN quantum well and holes weakly localized due to potential fluctuations.

The feasibility of producing channel waveguides in crystalline layers of YAG:Tm,Nd, epitaxially deposited on YAG crystals is explored. The guided blue luminescence is studied under infrared excitation at 785 nm ([Tm.sup.3+] absorption) and 808 nm ([Nd.sup.3+] absorption) for the epitaxial planar waveguides of different [Tm.sup.3+] and [Nd.sup.3+] concentrations for all the implanted channel waveguide structures.

The GaAs and AlAs thin capping layers as well as postgrowth rapid thermal annealing (RTA) are applied to InAs quantum dots (QDs) fabricated by molecular beam expitaxy to study the tunability of optical properties of QDs by photoluminescence (PL) methods. The observed single PL peak for GaAs-capped QDs and double-peak PL spectrum for AlAs-capped QDs could be used as a guideline to select only the smallest QDs enhanced by postgrowth annealing.

The V/Al/V/Ag metallization is adapted to other compositions of n-[Al.sub.x][Ga.sub.1-x]N and it has provided low specific contact resistances as well as smooth surfaces on both n-GaN and n-[Al.sub.0.58][Ga.sub.0.42]N. The measurements of the specific contact resistance as a function of temperature have shown that field emission is the dominant current transport mechanism in low resistance Ohmic contacts to n-GaN and n-[Al.sub.0.58][Ga.sub.0.42]N.

The full potential linearized augmented plane wave method with the generalized gradient approximation is used to study the electronic structure, chemical bonding, and optical properties of rhombohedral LaAl[O.sub.3]. The results provide insight into the discrepancy between the optical band gap and the direct band gap due to the limitation of the selection rules in the interband transitions.

The electrochemical capacitance-voltage (ECV) and the secondary ion mass spectroscopy (SIMS) were measured to verify the origin of the surface concentration peak present in doping profiles of screen-printed Al-[p.sup.+] regions. The results showed that after the removal of the residual Al-rich silicon surface structures, the Al concentration peak at the surface measured by ECV and SIMS completely disappeared.