Low-temperature photoluminescence of undoped and moderately δ-doped Si1−xGex/Si (x < 0.1) quantum wells has been studied. The influence of boron δ-layer on the excitonic luminescence and the luminescence caused by a dense electron plasma was demonstrated. The conditions under which the luminescence spectra of quantum wells are dominated by impurity-bound excitons (BE) have been established. Some unusual properties of these BE are explained in terms of type II band-offset in Si1−xGex/Si (x < 0.1) quantum wells, which favors a spatial separation of electrons and holes. It is shown that the temperature dependence of an excitonic emission in the quantum wells allows to calculate the BE-related density of states and, thus, can be used for contactless estimation of the impurity concentration in quantum wells.
It is shown that, at helium temperatures, relaxed CdTe films reveal isolated emitters, the properties of which indicate their relation with a weakly perturbed fragment of the Shockley dislocation core. The polarization and spatial distribution of such emitters in CdTe/Si and CdTe/GaAs virtual substrates contain information on the structure of extended defects in a relaxed CdTe layer, which are important for HgCdTe epitaxy.
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