The effect of rapid thermal annealing (RTA) on the shapes of silicon dioxide capped symmetric coupled double GaAs/AlGaAs quantum wells (CDQW) has been investigated. In contrast to previous results on single quantum wells in which increases in exciton energies were observed after RTA, large decreases in exciton energies were seen in CDQWs. Furthermore, there was clear evidence, in the excitation spectrum and in increases in the lowest energy exciton lifetime, of asymmetry present in the heterostructure after RTA.

The transient phenomenon in carbon-doped AlGaAs/GaAs HBT's has been found to reoccur after a brief thermal annealing under no bias. The temperature and the current dependencies have been studied with HBT's made with MOCVD grown wafers. The experimental data ran be explained by a model based on thermal decomposition of C-H complexes during annealing and electron captures by hydrogen ions under minority-carrier injection.

A technique that makes it possible to transfer semiconductor epitaxial films from a lattice-matched growth substrate to a host substrate of a different material is discussed. The transfer of epitaxial films allows materials with different lattice constants to be bonded together without generating a substantial number of defects in regions that are critical to device operation. The thin-film transfer process utilizes metallic solder as an interface between the transferred semiconductor layers and the host substrate. In this transfer process. the film is rigidly supported at all times during transfer, providing the potential for defect-free large-area films. The fabrication of InGaAsP lasers on both GaAs and Si substrates is described. Measurements of the optical characteristics of the lasers show threshold currents comparable to those of conventional lasers

The effect of rapid thermal annealing (RTA) on the shapes of GaAs/AlGaAs quantum wells (QWs) has been investigated by monitoring exciton energies using low temperature photoluminescence and photoluminescence excitation spectroscopies. After RTA, large changes in exciton energies were observed only in regions of the samples in which excess surface vacancies were generated, either by capping with a thin layer of SiO2 or by low-energy ion implantation. These changes were interpreted as resulting from modifications of the shapes of the as-grown QWs from abrupt or square to gradual (rounded) due to enhanced interdiffusion of well/barrier atoms. For single QWs there was an increase in exciton energy whose magnitude depended on the width of the well, its distance from the surface of the wafer, the annealing temperature and the total number of surface vacancies available. From studies of coupled QWs, there was clear evidence of asymmetry in the heterostructure after RTA. Although both techniques of vacancy generation yield substantial QW shape modifications, the ion implantation technique has the advantages of being highly reproducible and of being compatible with any material system.

GaAs/AlGaAs quantum wells (QWs), selectively intermixed by SiO2 capping and rapid thermal annealing, have been characterized on a microscale using spatially resolved photoluminescence (PL) spectroscopy. From the evolution of the PL spectra across the boundary between the unmixed and intermixed regions, it was concluded that the transition region is narrower than the 1.5 μm excitation beam diameter. The magnitude of the intermixing was also found to increase with the thickness of the oxide. The present intermixed QWs were found to be stable against subsequent thermal treatment below the temperature limit imposed by the intrinsic interdiffusion. These results demonstrate that the effective band gap of QWs, and their physical properties, can be adjusted by controlling the oxide thickness profile.

Evidence has been obtained indicating asymmetry in the shapes of as-grown symmetric coupled double GaAs/AlGaAs quantum wells (CDQW) which were modified by capping with silicon dioxide followed by rapid thermal annealing. The sensitivity of the optical properties of CDQWs to perturbations, in contrast to single quantum wells, permitted this observation. The asymmetry may result from the thermally driven unidirectional diffusion of vacancies generated near the surface which enhances intermixing of barrier and well materials in the quantum wells.

The effect of rapid thermal annealing (RTA) on the shapes of single and coupled double GaAs/AlGaAs quantum wells has been investigated by measuring exciton energies using low temperature photoluminescence and photoluminescence excitation spectroscopies. After RTA, large changes in exciton energies were observed only if the sample was capped with a thin layer of silicon dioxide. For single quantum wells there was an increase in exciton energy whose magnitude depended on the width of the well and its distance from the surface of the wafer. For coupled quantum wells, the exciton energy decreased and there was clear evidence, in the excitation spectrum, of asymmetry in the heterostructure after RTA.

A spatially selective technique for modifying exciton energies in quantum wells by employing rapid thermal annealing and silicon dioxide capping is demonstrated in the InGaAs/AlInAs material system. Exciton emission energies in these quantum wells are blue shifted by as much as 60 meV after a 15 s rapid thermal anneal above 800 °C. The dependence of the energy shift on well width and annealing temperature is studied by measuring low-temperature photoluminescence spectra of single quantum wells. In contrast to the GaAs/AlGaAs case, a silicon dioxide film deposited on the surface inhibits the energy shift suggesting that a different mechanism is operating in the present material system.

We report the observation of 5 K photoluminescence (PL) spectra of undoped GaAs, grown by molecular beam epitaxy, which are dominated by free exciton (intrinsic) emission. The weakness of impurity related features is taken as an indication of very low levels of residual impurity contamination. The identification of the strong, narrow peak in the PL spectra with the free exciton emission has been confirmed using magnetophotoluminescence studies. Our results are in good agreement with magnetoreflectance data which are sensitive only to intrinsic (i.e. excitonic) features.

We report the observation, in the low temperature photoluminescence excitation spectra of high quality GaAs/AlGaAs single quantum wells, of distinctive peaks arising from the first excited level (2s) in addition to the ground state (1s) of heavy- and light-hole excitons. We utilize the accurate determination of the 2s-1s splitting energy, made possible by this observation, to derive the binding energies of the heavy- and light-hole excitons as a function of well width and find good agreement with other similar determinations and with recent theoretical calculations based on models of quantum wells with valence band coupling. The agreement with exciton binding energies derived from magneto-optical spectroscopic experiments is unsatisfactory and suggests that further work in the interpretation of the magneto-optical experimental spectra is required.

We report the first observation of a narrow, low temperature photoluminescence peak associated with the presence of a two-dimensional electron gas (2DEG) at a GaAs/AlGaAs heterointerface. The exact physical mechanism giving rise to this emission is not clear. However, based on a large number of samples, its intensity is found to be directly related with the concentration of the electron gas. The temperature and exciting-intensity dependencies of the peak are consistent with a model based on free excitons in GaAs bound to the electron quantum well formed at the heterointerface by the 2DEG.

We report on detailed photoluminescence (PL) and photoluminescence excitation (PLE) studies of GaAs/A1GaAs single quantum wells (SQW) with differing well widths measured over temperatures ranging from 5K to 300K. A new trapping phenomenon was observed at low temperatures, which affects the linewidth and PL intensities (radiation lifetimes) of free excitons in the SQWs and which is related to the formation of bound excitons. At higher temperatures, excitonic linewidths were primarily broadened by optical phonon scattering. The temperature dependencies of the excitonic energies of SQWs were similar to that of bulk material and were independent of the quantum well width.

We report the observation of a low temperature photoluminescence peak associated with the presence of a two-dimensional electron gas (2DEG) at a GaAs/AlGaAs hetero-interface. The exact physical mechanism giving rise to this emission is not clear. However, based on a large number of samples, its intensity is found to be directly related with the concentration of the electron gas. The temperature and exciting-intensity dependences of the peak are consistent with a model based on GaAs excitons bound to the electron quantum well formed at the heterointerface by the 2DEG.

A gate probe method has been developed to accurately determine source, drain, and channel resistances of MESFET's. The method employs the gate current crowding phenomenon at higher drain currents. An exact equation was derived for the resistances whose fit to the data provides a self-consistent check of the determined parameters.

Nominally undoped p-type GaAs with an unusually low shallow donor concentration has been grown by molecular beam epitaxy. The effect of the As/Ga flux ratio on the residual shallow donor and acceptor concentrations and defect density in this material was investigated by analyzing low temperature photoluminescence (PL) spectra. The PL spectra are indicative of low shallow donor concentrations, since they exhibit a single, narrow (FWHM=0.4 meV) free exciton peak and essentially no donor-related peaks. For increasing As/Ga flux ratio the donor concentration decreases, the defect concentration increases, and the acceptor concentration goes through a minimum. These results can be explained by a model based on the incorporation of Si and C into As and Ga sites and the formation of a carbon–Ga vacancy defect complex.

A method based on monitoring the thermally stimulated drain conductance (TSDC) under trap filling and emptying bias-temperature sequences is developed for directly characterizing high defect density AlGaAs layers in high electron mobility transistors (HEMT's). The rate equation for trapped electron emission is solved for the conditions pertinent to the TSDC method. Measured results on HEMT's are in excellent agreement with this solution and compare favorably with values reported by others. TSDC is as convenient to implement but more applicable than deep-level transient spectroscopy (DLTS) for the high concentration of AlGaAs defects normally encountered in HEMT's.

The I-V characteristics of MBE-grown AlGaAs/GaAs high electron mobility transistors (HEMT's) are studied using a bias and temperature sequence between 77 and 300 K to control trap occupancy. Low-temperature threshold voltage, transconductance, and saturation current are found to be either increased or decreased significantly relative to their 300 K values depending on the gate bias condition during cool down. This behavior is shown to be caused by variations in trap occupancy in the highly doped AlGaAs layer.

Complete dielectric isolation of silicon regions 45 μm wide for microcircuits on silicon substrates is demonstrated by selective formation of oxidized porous silicon in heavily doped n-type regions. Anodic etching of n-type silicon in a hydrofluoric acid electrolyte exhibits a concentration-dependent voltage threshold. This voltage dependence allows the porous silicon formation process to be selective to heavily doped regions and self-stopping on lightly doped regions. Rapid oxidation of this porous silicon yields an oxide with dielectric properties approaching those of standard thermally grown silicon oxides. This process is an improvement over previously reported processes utilizing porous silicon in that wider regions (up to 300 μm) are dielectrically isolated by an oxide whose thickness is controllable and uniform so that stress and wafer warpage are minimized.

A constant voltage scaling scheme is examined for the enhancement of frequency and power performance of FETs. For low electric fields, this scheme is self-consistent within Shockley's formulation and improves the overall frequency and power performance figure of merit by a factor of κ 6 with a κ times reduction in the device area. For high electric fields, the improvement is reduced to κ 3 times due to the velocity saturation effect. Reduced breakdown voltage further limit the improvement.