Raman spectroscopy and photoluminescence of ZnTe thin films grown on GaAs

Abstract

We report resonant Raman scattering and photoluminescence (PL) measurements on two ZnTe thin films grown by molecular-beam epitaxy on GaAs substrates with thicknesses around 0.5 and 1.0 μm. The data have been obtained by using the different excitation energies of an Ar+ laser to distinguish Raman from PL and analyze resonant effects. The characteristic features of the low-temperature PL spectra are the light and heavy free exciton emissions, split due to the thermal strain effect, followed by several phonon replicas of these lines. Moreover, longitudinal and transversal polariton splittings of heavy excitons are clearly observed. Their reduced masses have been obtained from the exciton binding energies. Room and low-temperature Raman spectra show, besides the typical longitudinal optical (LO) multiphonon emissions, forbidden zone-center transverse optical (TO)+(n−1)LO phonon combinations, which yield an accurate value for the LO and TO phonon energies. The breakdown of the selection rules is attributed to surface faceting.