Photoreflectance and piezophotoreflectance studies of strained-layer ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As-GaAs quantum wells

In this paper we present an investigation of the optical transitions in strained ${\mathrm{In}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As-GaAs single and multiple quantum wells, for indium content x≃10% and 20% and various well widths. The uniaxial stress dependence of reflectance and photoreflectance spectra permits unambiguous assignment of the experimental features to electron-heavy-hole and electron-light-hole excitonic transitions. Calculated transition energies are compared with the measured values. In these calculations, in the envelope-function formalism, the misfit-strain-induced coupling between the ${\mathrm{\Gamma }}_8$ light-hole and the ${\mathrm{\Gamma }}_7$ split-off valence bands is taken into account and the valence-band offset ratio is chosen as an adjustable parameter. By fitting all the experimental results to our calculations, the heavy-hole valence-band offset fraction ${\mathit{Q}}_{\mathit{v}\mathit{h}}$ is determined to be about 0.34. This implies that these quantum wells are type I for the electron-heavy-hole system and type II for the electron-light-hole system, with the electrons and the heavy holes confined in the ${\mathrm{In}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As layers and the light holes in the GaAs barrier regions.