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Low-temperature excitation and photoluminescence spectra are described for single GaAs/Al0.37Ga0.63As quantum wells grown by molecular beam epitaxy with and without a 2-min interruption of growth at the heterointerfaces. The spectra from samples grown with interruption include well-resolved multiple sharp peaks which are due to changes in well thickness of one monolayer and to bound excitons. These peaks are as narrow as 1.0, 1.7, and 6.0 meV for single wells of width 57, 28, and 17 Å, respectively. [ABSTRACT FROM AUTHOR]

High quality GaAs/AlxGa1-xAs single and multiquantum well heterostructures were grown for the first time by chemical beam epitaxy. Studies using low-temperature photoluminescence and excitation spectroscopy techniques show that on the average these samples are similar in quality to similar structures from this laboratory grown by molecular beam epitaxy (MBE) and in certain specific characteristics superior to the MBE ones. Furthermore, in some important respects, they are also superior to those grown by organometallic chemical vapor deposition (OMCVD). The very small red shifts observed between emission and n=1 exciton transition E1h with continuous growth show that the emission is dominated by E1h excitons. An interface roughness of δL<=±a/2, where a is the lattice constant, and very square wells (undistorted) even with continuous growth, in contrast to OMCVD are inferred from the excitation spectra. Unusually sharp exciton transition peaks up to E3h including forbidden transitions were obtained in single quantum wells. Such high quality line shape has not been obtained in MBE or OMCVD grown wafers so far. The excitation spectra also show no evidence of band filling due to holes or electrons from the AlxGa1-xAs layers which is a common problem with the OMCVD technique. From this study, it is also shown that the GaAs and AlxGa1-xAs materials are of very high purity. [ABSTRACT FROM AUTHOR]

GaAs-AlxGa1-xAs single and multiquantum well structures grown by metalorganic chemical vapor deposition have been examined for the first time in detail using low-temperature photoluminescence, cathodoluminescence, and transmission electron microscopy. The better heterointerfaces are very uniform with a large scale roughness of approximately plus or minus a monolayer along the interface on a scale of the exciton diameter or larger and a composition gradient width of less than three monolayers across the interface. The GaAs well interface roughness and associated impurity luminescence are not very sensitive to the thickness of the AlxGa1-xAs prelayer. With nonoptimum growth conditions, the quantum well photoluminescence characteristics suggest a substantial amount of band filling due to holes presumably from the AlxGa1-xAs layers. [ABSTRACT FROM AUTHOR]

A correlation has been demonstrated between impurity trapping and the interface structure in GaAs quantum well (QW) superlattices and single quantum well structures grown by molecular beam epitaxy (MBE) on (100) GaAs. Using low-temperature cathodoluminescence, photoluminescence, and transmission electron miscroscopy, we have shown that interface roughness in QW superlattices is related to trapped impurities at interfaces. We have observed that impurities originate from either the substrate or from the GaAlAs MBE layers. A new getter smoothing effect associated with QW structures is shown to produce efficient impurity trapping and yield higher quality GaAs QW with atomically smooth interfaces. [ABSTRACT FROM AUTHOR]

We report growth of ultrapure GaAs by molecular beam epitaxy (MBE) and show that the arsenic source has a dramatic effect on the purity. With every thing else the same, by changing the arsenic source from 6N grade double refined chunks to a 7N grade slug which closely fits the 35 cm3 crucible, the deep electron trap and the residual acceptor densities were reduced by nearly two orders of magnitude. When intentionally doped with Si to an electron density of 3×1013 cm-3, the measured mobility at 77 K was 205 600 cm2 V-1 s-1, which increased to 294 700 cm2 V-1 s-1 at 42 K. These mobilities are the highest ever observed in intentionally n-doped MBE GaAs. Low-temperature photoluminescence studies of both undoped and Si-doped GaAs layers grown with the As slug show a marked decrease in acceptor- and defect-related luminescence over that observed when the As chunks are used. Our study conclusively proves that the major source of residual acceptor impurities and typical MBE GaAs traps observed by deep level transient spectroscopy is the chemical impurities present in the arsenic source, although the exact nature of these impurities is yet to be identified. These impurities or their complexes with the native crystal defects, and not the native defects alone, are responsible for the deep traps. [ABSTRACT FROM AUTHOR]

Photoluminescence spectra from Al0.37Ga0.63As/AlAs multiple quantum well structures with staggered band alignments are presented which provide the first direct optical measure of the valence-band offset at a semiconductor heterojunction. The experiment takes advantage of the crossover occurring at a critical aluminum concentration above which the indirect X minima in the AlAs become the lowest energy conduction bands in the system, and recombination occurs across the interface. The resulting emission fixes the valence-band offset at ΔEv =342±4 meV for this structure. [ABSTRACT FROM AUTHOR]