<i>X</i>-point excitons in AlAs/GaAs superlattices

Abstract

We have found a long-lived emission at low temperatures in AlAs/GaAs superlattices with approximately equal thicknesses of AlAs and GaAs and with periods in the range 18–60 Å. The emission shows the nonexponential time decay characteristic of an indirect exciton made allowed by disorder. The exciton is found to be at the zone boundary, and to consist of a Γ hole localized in the GaAs and an AlAs X-point electron. The disorder is at the AlAs-GaAs interfaces. There is no ‘‘camel’s back’’ in the exciton dispersion.