Identification of valence subbands in CdTe-${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Zn}}_{\mathit{x}}$Te strained-layer quantum wells by differential spectroscopy

Wavelength-modulated reflectivity and piezomodulated reflectivity investigations have been made at 6 K on a series of CdTe-${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Zn}}_{\mathit{x}}$Te (x≃0.08 and 0.13) strained-layer single quantum wells grown on ${\mathrm{Cd}}_{1\mathrm{-}\mathit{y}}$${\mathrm{Zn}}_{\mathit{y}}$Te substrates (y∼0.04). The reflectivity patterns exhibit a rich series of structures which are unambiguously identified in terms of ‖3/2;± 3) / 2 〉 (heavy-hole) or ‖3/2;±1/2〉 (light-hole) excitons. Comparison between wavelength-modulated and piezomodulated data enables us to identify the quantum-well-related transitions as transitions of type-I nature between ground and excited conduction and heavy-hole valence subbands. This has been obtained for a series of quantum-well widths ranging from 50 up to 450 Å. Our findings are consistent with a small value of the CdTe-ZnTe zero-strain valence-band offset. The calculated light-hole-related transitions, which we did not observe in reflectivity when x∼0.08 but were detected when x∼0.13, are then found to have a type-II nature.