RESONANT RAMAN-SCATTERING WITHIN AN INHOMOGENEOUSLY BROADENED EXCITON BAND IN SEMICONDUCTORS

We report on resonant Raman scattering (RRS) by LO-phonons, which is mediated by excitons in two semiconductors: (a) Bulk GaP containing isoelectronic nitrogen impurities. (b) CdTe/ZnTe superlattice (SL). In both cases a strong RRS is observed upon excitation within an inhomogeneously broadened exciton band. In GaP this band is due to N-bound excitons which are perturbed by other distant impurities (V band). In the SL the band is that of intrinsic excitons which are subjected to random potential fluctuations arising from strain and interface roughness. We use a model based on the dependence of the exciton damping on its energy in order to fit the RRS profile to the observed data (at T = 2 K). The sources of damping are identified: for GaP: N these are exciton tunneling between perturbed states and thermal excitation into the non-perturbed N-bound exciton band. For the SL these are tunneling between localized states and scattering between extended states. It is thus demonstrated that RRS provides a method for studying the spectral consequences of exciton dynamics in weakly disorderd semiconductors, which is complementary to other time-resolved spectroscopic methods. © 1990.