Evidence of type-I band offsets in strained ${\mathrm{GaAs}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Sb}}_{\mathit{x}}$/GaAs quantum wells from high-pressure photoluminescence

We have used high-pressure photoluminescence in a diamond-anvil cell to investigate the band offsets between strained ${\mathrm{GaAs}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Sb}}_{\mathit{x}}$ and unstrained GaAs for x=0.12. It has generally been expected that this system should display a strongly type-II band lineup, with holes confined in deep ${\mathrm{GaAs}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Sb}}_{\mathit{x}}$ wells and the lowest-energy electron states in GaAs. Our results on a multiple-quantum-well sample show that this is not the case. We measure the photoluminescence transition energies up to and beyond the Γ-X crossover near 36 kbar, where the luminescence becomes indirect. The character of the Γ-X crossover dependence on well width requires a type-I offset for the X minimum and suggests a type-I offset for the Γ minimum of the conduction band. This is in good agreement with theory when the strong band-gap bowing in the ${\mathrm{GaAs}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Sb}}_{\mathit{x}}$ alloy system is properly taken into account.