Pressure-induced conduction-band crossover in a ZnSe/${\mathrm{ZnS}}_{0.18}$${\mathrm{Se}}_{0.82}$ symmetric superlattice

We have measured low-temperature photoluminescence spectra of a ZnSe/${\mathrm{ZnS}}_{0.18}$${\mathrm{Se}}_{0.82}$ symmetric superlattice at hydrostatic pressures up to 8 GPa. A crossover of the Γ-like conduction-band states of barrier and well near 4.5 GPa is evidenced by the pressure dependence of the intensity of the main emission band which corresponds to the localized exciton of the ZnSe wells. Further support for a type-I to type-II conversion comes from the formation of a type-II exciton transition, where the excited electron state is confined in the alloy layers, and also from the observation of a ZnSe-like phonon sideband characteristic of the barrier material. The conduction-band crossover is an indirect confirmation of the small conduction-band offset in the ZnSe/${\mathrm{ZnS}}_{\mathit{x}}$${\mathrm{Se}}_{1\mathrm{-}\mathit{x}}$ superlattices.