Localized indirect excitons in a short-period GaAs/AlAs superlattice

We have studied the optical properties of a short-period superlattice composed of 20.4-A\r{} GaAs and 14.7-A\r{} AlAs layers. The superlattice behaves as an indirect-gap material. A slow and nonexponential decay of the luminescence can be interpreted as the emission from the \ensuremath{\Lambda} indirect excitons localized at the GaAs/AlAs interfaces. The temperature dependence of the exciton decay time can be explained in terms of a transition by phonon-assisted tunneling, followed by a nonradiative transition.