Light- and heavy-hole free-exciton transitions in narrow ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs quantum wells

Photoluminescence measurements were made on narrow ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs single-quantum-well structures with nominal x values of 0.10 and well widths ranging from 2 to 17 monolayers (ML’s). Transitions due to the collapse of heavy-hole free excitons and light-hole free excitons as well as the usual GaAs band-edge transitions are observed. The measured transition energies are compared with results of band-structure calculations of the light-hole and heavy-hole subband energies for various assumed relative valence-band-offset values. A detailed comparison between the measured and calculated results suggests that the light hole is only marginally, if at all, confined in the 2-, 4-, 6-, and 10-ML wells. Inconclusive results are obtained for the 17-ML well because of an uncertainty in its exact x value. These results directly imply an upper limit of 0.4 for the relative valence-band offset for pseudomorphic ${\mathrm{In}}_{0.10}$${\mathrm{Ga}}_{0.90}$As/GaAs on GaAs(001) heterojunctions. Also reported is a strong dependence of the difference in the calculated light-hole and heavy-hole subband energies on both the indium content and the assumed valence-band offset.