Photoluminescence spectra of GaAs quantum wells of widths 26 to 150 A are studied as a function of hydrostatic pressure (0 -70 kbar) at 80 and 150 K. The pressure coefficients of both the heavy-and light-hole excitons are found to decrease with decreasing well width. The direct to indirect conduction-band crossover, leading to the formation of type-II heterostructures, occurs at higher pressures for wider wells. A transition associated with the X conduction band in quantumwell structures is observed and its pressure dependence is established. Correlating this transition to barrier-to-well recombination determines the valence-band offset.

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The presence of a nonrandom fractional number of atomic planes in each layer of a superlattice produces unusual diffraction patterns in which the peaks cannot be indexed in the usual fashion as due to a single series. The x-ray line broadenings are distinctly different from earlier measurements and calculations in which the interfacial roughness is due to random variations of the scattering function. Therefore, interfacial roughness encountered at a single interface may just be a consequence of controlled, but not random, roughness and that under proper growth conditions superlattices with atomically sharp interfaces may be produced. These results are in good agreement with experimental measurements.

Reflectance experiments on GaAs/Ga1−xAlxAs single quantum well structures were performed at 4.2 K, with different thicknesses of the front GaAlAs barrier layer (100–1000 Å). The observed exciton reflectance line shapes depend strongly on the thickness of the front barrier layer due to the interferences between the reflected waves from the front surface and the quantum well interfaces. Calculations of the reflectance line shapes show good agreement with the observations. The absorption coefficient for the electron heavy-hole exciton transition in a single quantum well sample is determined. Our study also provides a new understanding of the line shapes measured in photoreflectance experiments.

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