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Analysis of carrier relaxation and capture in narrow quantum wells (QWs) using a Monte Carlo method shows that the capture is longer for narrow quantum wells, and the QWs have relaxation times in the 10-15 ps range. Slow phonon emission is due to the two-dimensional state density and electron-phonon interactions. Narrow QWs restrict the overall laser performance.

Theoretical and experimental study of the spreading of defects in semiconductor heterostructures reveals that defects created by latticed-matched regions can be prevented from entering the pseudomorphic layer. The spreading of defects can be controlled by pseudomorphic layers. The study also involved the experimental investigation of pseudomorphic InGaAs layers and their influence on the photoluminescence intensities of AlGaAs/GaAs quantum wells. The defects below the quantum well and silicon implantation is generated by GaAs substrates of higher etching pit density.

The lattice constant, strain relaxation, thickness and critical thickness of a thin In(sub x)Ga(sub 1-x)As layer embedded in GaAs is determined by the double crystal x-ray rocking curve technique. The X-ray data over a wide scan angle is measured and analyzed, which enables the simultaneous determination of buried layer thickness and strain. The dynamical diffraction theory is used in the analysis of the results of the measurement. The critical thickness for an In(sub x)Ga(sub 1-x)As layer embedded in GaAs determined from X-ray data, is greater than the critical thickness predicted by the force balance model.

The temporal response characteristics of high-speed photodiodes with GaAs/AlGaAs multiquantum well absorption/transit regions were investigated. The results showed that the response time of devices with AlGaAs barriers was only slightly affected by theapplied reverse bias. However, devices which had barriers greater than 0.1 weresensitive to applied bias. This indicated that high-speed optoelectronic devices can be made with multiquantum well absorption regions with small barrier heights.

The molecular beam epitaxial growth and characteristics of silicon-doped AlGaAs and GaAs on (311)A GaAs substrates and their device applications were investigated. The results showed that Si was a good amphoteric dopant in GaAs and AlGaAs with (311)A orientation. Varying the molecular beam epitaxial growth conditions allowed the doping conductivity of Si in GaAs and AlGaAs to be controlled in a reproducible manner. The combination of high growth temperatures and low flux ratios induced the Si atoms to act as uncompensated acceptors. On the other hand, low growth temperatures and high flux ratios induced the Si atoms to behave as donors.

A voltage tunable logic gate based on the multiquantum-well heterojunction bipolar transistor (MQW-HBT) is developed for multifunction logic applications. The MQW-HBT gate consists of multiple inputs and is capableof handling complex logic functions, such as multiplexing and pattern recognition, aside from the common logic functions. It relies on the quantum confined Stark effect for the achievement of these multiple logic functions.

Detailed measurements of high-field transport properties of pseudomorphic InAsP/InP modulation doped heterostructures grown by low-pressure organometallic chemical vapor deposition were made at 300 and 77 Kelvin. Results show that high-field channel velocities are comparable with that of InGaAs/InAlAs heterostructures. The transport properties of InAs/InP also indicate that carriers remain confined in the channel even at high fields.

Gas-source molecular beam epitaxy was successfully used to grow SiGe alloys using Si2H6 and GeH4. Perfect crystallinity and surface smoothness were achieved with alloys having an x value less than 0.3. Epilayers with Ge composition of up to 33% were produced at 610 degrees celsius, presently the lowest temperature ever used for gas-source SiGe molecular beam epitaxy. An increase in growth rate was also observed whenever the Ge composition of the alloys was increased.

n-type doping of SiGe and Si with phosphine during gas-source molecular beam epitaxy does not affect the growth rate of Si and SiGe. Activation of the induced phospine atoms occurs even in the absence of ex situ annealing. A phosphine and boron doping junction in the layers exhibits characteristic doping profiles and rectifying properties.

Electron and hole impact ionization coefficients in biaxially strained InxGa1-xAs/InyAl1-yAs(0.44

The alpha and beta impact ionization coefficients for electrons and holes in pseudomorphically strained In0.2Ga0.8As and In0.15Ga0. 63Al0.22As channels embedded in Al0.3Ga0.7As were determined. The results showed that the impact ionization coefficients in lattice matched GaAs layers were lower than those in strained materials. In all samples investigated, the beta coefficient was larger than the alpha impact ionization coefficient.