Photoluminescence study of undoped and modulation-doped pseudomorphic AlyGa1−yAs/InxGa1−xAS/AlyGa1−yAs single quantum wells

Abstract

Photoluminescence has been used to describe the dominant recombination processes in undoped pseudomorphic GaAs/${\mathrm{In}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As/GaAs single quantum wells for x<0.17. The temperature and intensity dependences of the photoluminescence indicate emission arising from both donor-bound and free excitons in all well widths studied (6–160 Å). No evidence for the presence of monolayer fluctuations has been seen despite the high optical quality of the excitonic features. By recording photoluminescence excitation spectra as a function of well width it has been possible to unequivocally identify peaked excitonic absorption spectra with absorption transitions involving light-hole states. Comparisons of absorption energies with calculations of confined levels that include strain suggest that the light-hole state is not confined in the ${\mathrm{In}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As well. Modulation-doped ${\mathrm{Al}}_{\mathit{y}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{y}}$As/${\mathrm{In}}_{\mathit{x}}$ ${\mathrm{GA}}_{1\mathrm{-}\mathit{x}}$As/GaAs structures are shown to be ideal systems for studying the optical properties in the presence of free carriers. With increasing carrier concentration the excitonic luminescence from the well broadens, and at the highest carrier concentrations occupation of n>1 conduction-band states is clearly revealed by the presence of a high-energy emission.