Thickness dependence of exciton and polariton spectra from ZnSe films grown on GaAs substrates

Abstract

ZnSe films with thicknesses from 0.05 to 1.45 μm were grown on GaAs substrates by molecular beam epitaxy. Low temperature photoluminescence (PL) and reflectance spectra are presented to show the thickness dependence of the exciton and polariton properties in the films. In addition to sharp PL peaks from free and donor bound excitons, an acceptor bound exciton peak was observed in the thin films and its intensity decreases rapidly with the film thickness. The PL characteristics show the acceptor centers being the defect states near the ZnSe/GaAs interface. The classical theory of exciton–polaritons was used to calculate the reflectance spectra and compared to the measured results. The comparison reveals the effects of strain, surface, and interface on the reflectance spectra from both heavy- and light-hole excitons. In addition to the strain-induced light- and heavy-hole splitting, the light-hole excitons show a larger damping and less sensitivity to the surface dead layer than the heavy-hole excitons. When the film thickness increases, the interference effects become more important and the contribution from the excited exciton states to the reflectance spectra may no longer be negligible.