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A series of high-mobility [Al.sub.0.12][In.sub.0.88]Sb/InSb heterostructures are grown by molecular beam epitaxy to examine the fabrication of micro-Hall magnetic field sensors. The results have shown that the utility of devices with larger devices has led to magnetic field detection in the pT range at low temperatures and sub-nT range even at room temperature.

A charge control model is developed for the transient analysis of the bipolar transistor laser in forward active mode in order to describe the dynamics of electron, photon and charge densities. The analysis of laser switching has shown that the turn-on time is reduced by increasing the base current or decreasing the spontaneous emission lifetime of electrons in the quantum well.

A complete analysis of the enhancement taking place in the hole confinement in the GaInAsN-aAsSbN thin double-layer quantum-well structure is presented. The electrons are shown to be less confined as carriers, in comparison to the bilayers structure.

The carrier transfer between quantum dot (QD) and quantum well (QW) layers is analyzed in a hybrid dot-well system based on InAs QDs and InGaAs QWs. Strong state-filling effects of the excited QD states have affected the carrier transfer efficiencies.

Several theoretical studies are conducted to explain the application of the different staggered quantum well structures for enhancing the output power and performance of the blue InGaN light-emitting diodes. The optimum design of the staggered quantum well required for taking out the best optical characteristics of these diodes is also discussed.

A new optoelectronic measurement of quantum well (QW) thickness is described and it is applied to doped and undoped [In.sub.0.53][Ga.sub.0.47]As/[In.sub.0.52][Al.sub.0.48]As multiple-QW structures. The QW thicknesses have agreed well with the QW thicknesses estimated by double-crystal x-ray diffraction within almost two monolayers, which are used for determining the distance of potential boundaries confining the electron wave functions.

Several studies are conducted to explain the photoluminescence and emission variation exhibited by the different InAs quantum dots coupled with the symmetric quantum wells. The various factors leading to differences in the emission intensities are also identified.

Several nanotexturing InGaN/GaN multiple quantum wells are employed to explain the relaxation taking place in the lattice-mismatched strain by deep postetching. The various effects of the strain on the optical properties are 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.

Microdisk and microstadium resonators based on InGaAsP multiquantum-well laser structures are prepared by focused ion beam by using [Ga.sup.+] ion milling and polishing followed by selective chemical etching. The mode selection dependence with the surrounding index of refraction is described for chemical sensing applications.

Two types of devices with the same fabrication procedures except for the growth conditions for the InGaN quantum wells (QWs) were examined to study the degradation of GaN-based light-emitting diodes due to high dc current stress. The data show that an increase in the growth rate in the InGaN layer led to the domination by the step flow growth mode over the spiral growth mode in the MQWs.

The emission intensity of GaInN quantum well structures with varied electron and hole wave function overlap were analyzed by temperature and excitation power dependant and time-resolved photoluminescence to determine the parameters which affect the internal quantum efficiency of GaInN quantum well structures. The temperature dependent photoluminescence emission intensity for thick polar quantum wells could be partially assigned to increased screening effects and higher quantum well barriers for thicker quantum wells.

A model is designed for describing the shape of the spontaneous emission spectrum from a quantum-well structure and it is applied to the spectra of AlGaInP light-emitting diodes. The studies have shown that the probability distribution functions are almost Gaussian and the emission spectra is described by an analytical expression with fitted parameters.

The magnetotransport properties of a gated [In.sub.0.53][Ga.sub.0.47]As/InP quantum well structure are studied in the presence of spin splitting when only one electronic subband is occupied. The studies have shown that larger quantum mobility is found for the higher-energy spin subband and the difference between the quantum mobilities for the two spin subbands is altered with the gate.

A numerical study is performed on the linewidth enhancement factor ([alpha]-parameter) in single and multiple-quantum-well structures built from [In.sub.0.38][Ga.sub.0.62][As.sub.1-y][N.sub.y]/GaAs material systems. The studies have shown that engineering the desired linewidth enhancement factor is possible by varying the parameters.

The temperature-dependent surface photovoltage spectroscopy (SPS) technique is employed to explain the characterization of the highly strained InGaAs/GaAs double quantum well (DQW) structures. The band lineup and several other properties of the structures are also analyzed.

The temperature dependence of excitonic properties for an InGaAs/GaAs p-i-n multiquantum well structure grown on a (111)B GaAs substrate by molecular-beam epitaxy is studied by using photoreflectance spectroscopy, in which the pyroelectric effect is considered. The optical-phonon energy and strength of electron-phonon coupling for the crystallographic directions of the material system, as well as the interface roughness from an analysis of the temperature dependence of PR broadening parameters are determined.

The optical characteristics of a nonpolar a-plane InGaN/GaN quantum well with different indium compositions, quantum well widths and injection carrier densities are discussed. The optimization condition is studied for designing the a-plane InGaN quantum well light emitting diode (LED) for applications, such as liquid crystal display backlight modules and lasers.

Microscopic theory in combination with a band structure calculation based on ten-band k*p theory specially formulated for highly strained materials are employed to explore the material properties of highly strained GaInNAs quantum wells grown on GaInAs or quasi-GaInAs substrates. The application of the lasers for high-temperature and high-speed operation is demonstrated based on the very high temperature [T.sub.0] and differential gain with moderate strain which are achieved by carefully designed quantum well structures.

InGaAsP quantum well (QW) structures are grown on an In[As.sub.0.21][P.sub.0.79] metamorphic substrate layer (MSL) deposited on an InP substrate. The samples with the MSL have displayed more intermixing either due to a higher diffusion or greater P-As exchange probability in the different composition QW and barrier layers when compared to the QW structure grown without the MSL and possibly influenced by the large reduction in phase separation.

A-plane [In.sub.x][Ga.sub.1-x]N/GaN multiple-quantum-wells (MQWs) samples are achieved by using r-plane sapphire substrates and optical quality is examined by using photoluminescence (PL) and time resolved PL measurements (TRPL). The results have shown that the indium content in a-plane InGaN/GaN MQWs has not only affected the optical performance, but is also important for application of nitride semiconductors.

Enhanced side-mode suppression in Bunimovich stadium lasers with strained InGaAs/InGaP quantum well (QW) active regions is described. The improvement in side-mode suppression is a consequence of coherent beating between orbits leading to a Vernier effect.

An optical study is used for analyzing the cuboidal single pillar microresonators with a quantum-dot-like emitter formed from local fluctuations in the InGaAs/GaAs quantum well potential. The quantum dot character of the lasing is confirmed in a temperature dependent experiment, which has indicated a number of emission intensity oscillations.

The band positions for [In.sub.x][Ga.sub.1-x]N/HaN heterointerfaces are calculated, which have directly correlated the positions of the bands with the band gap of InN and strain at the interface. The effects of strain have become very important as the mole fraction of In has increased, changing the band offset ratio.

A study is conducted to compare the structure and the photoluminescence (PL) properties of [In.sub.0.2][Ga.sub.0.8]As/GaAs quantum well (QW) structures grown on (311)-oriented substrates and the band gap temperature dependence of bulk [In.sub.0.2][Ga.sub.0.8]As. The sharp difference observed for the QW-exciton temperature from the band gap temperature dependence of bulk [In.sub.0.2][Ga.sub.0.8]As is attributed to temperature and well width dependent modification of the QW energy levels by the Stark effect.

[In.sub.x][Ga.sub.1-x]N/GaN (0.05

Selective area epitaxy is used to grow pyramidal GaN stripes followed by InGaN multiple quantum well (MQW) structures to produce long-wavelength green light emission. The redshifts obtained from the stripes due to enhanced delivery of indium species could find potential application to develop green and white light-emitting diodes and integrated photonic devices.

Two broadband semiconductor optical amplifier (SOA) devices containing tensile constrained quantum wells (QWs) are described. The In-rich conduction band to the heavy hole band (C-HH transitions) have gain from half the length of the SOA cavity, but they have broadened the spectral emission and reduced the gain efficiency at a given current.

The analysis of chemical changes determined from the quantitative comparison of intensity distribution across an interface in high resolution transmission electronic microscopy (HRTEM) images is described. Four different samples of InGaP/GaAs quantum wells grown with different interfacial schemes are characterized.

The development of an efficient algorithm that would account for nonparabolicity in carrier-carrier scattering in an ensemble Monte Carlo simulator is described. The results obtained for the electron dynamics in an InAs quantum well heterostructure showed that nonparabolicity significantly alters the transient regime as it increases the number of carrier-carrier scattering events.

The exciton spin relaxation times in [In.sub.x][Ga.sub.1-x]N/GaN multiquantum wells are studied as a function of well width and indium concentration for temperatures from 10 to 180 K. The results have shown that the fast exciton spin decay time is due to the influence of the holes via the exchange interaction and the temperature dependence is largely attributed to exciton-phonon scattering.

The effect of Rashba spin-orbit coupling for a series of two-dimensional electron gases in [In.sub.0.52][Ga.sub.0.48]As quantum wells, surrounded by [In.sub.0.52][Al.sub.0.48]As barriers, where either one or two electric subbands are populated is studied. The results are discussed with the consequences for spintronic devices operating on the principle of charge density dependent or electric field dependent spin manipulation in narrow band gap semiconductors.

The nanoscale InGaAs/InAlAs multi quantum well structures were used to analyze the nonparabolicity of the conduction band in [In.sub.0.53][Ga.sub.0.47]As. The results obtained from the method provide a direct means to determine the quantum well thickness.

The theoretical component of a combined experimental and theoretical investigation on electronic properties of InAs/GaSb-based quantum well systems is presented.