Photoluminescence and photoconductivity measurements on band-edge offsets in strained molecular-beam-epitaxy-grown ${\mathrm{In}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As/GaAs quantum wells

Structure has been observed in the photoluminescence and photoconductivity spectra of ${\mathrm{In}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As/GaAs (x≤1) strained quantum wells grown by molecular-beam epitaxy onto GaAs(001)-oriented substrates. Features in the spectra at energies larger than the energy gap of ${\mathrm{In}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As are interpreted as the allowed excitonic transitions between electron and hole subbands (including the strain-split-off valence band) in ${\mathrm{In}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As. The spectra were analyzed with the conduction-band offset and the energy gap of ${\mathrm{In}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As as adjustable parameters. No strain relaxation in quantum wells with thickness smaller than the critical one was observed. The strain-split-off valence subband in ${\mathrm{In}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As is found to be below the valence band of unstrained GaAs. The ratio of the conduction-band offset to the energy-gap discontinuity was determined to be 0.83±0.06.