Excitonic transitions in GaAsGaAlAs superlattices under a weak electric field

Abstract

We report a study of the photoluminescence spectra of GaAsGa 0.65Al 0.35As superlattice under an electric field of about 10 kVcm −1, from 9 K up to 80 K; the ratio ϱ = I −1 I 0 of the intensities of the −1 and 0 peaks of the Wannier-Stark ladder varies with the temperature T. To fit these variations, we assume for both transitions, a trapped exciton density of states with a gaussian distribution of eigenenergies, and a two dimensional density of states for free excitons. We show that above about 50 K there is a thermal equilibrium between direct and crossed free excitons whereas at low temperatures, the equilibrium statistics are not respected: the excitons trap into the direct state rather than to the crossed one.