Photoluminescence of disorder-induced localized states in GaAs/${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As superlattices

Purposely disordered GaAs/${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As superlattices, followed by an enlarged well, were grown by molecular-beam epitaxy. Selective-excitation photoluminescence measurements were performed to study the energy dependence of the motion of resonantly photocreated excitons in disordered superlattices. We report the existence of different energy regions in the superlattice bands, corresponding to extended and spatially confined (localized) states induced by disorder. The temperature dependence of the photoluminescence spectra suggests the existence of activation energies for the localized states. This reflects itself by an increase in the propagation rate of excitons by increasing the temperature. We compare qualitatively the experimental findings with a calculation of the superlattice miniband spectrum.