Angular dependence of resonant Raman and Rayleigh scattering in epitaxial ZnSe layers

In resonance with the lowest exciton states, the angular dependence of the cross-sections for one-longitudinal-optical-phonon Raman and elastic Rayleigh scattering is measured in ultrathin expitaxial layers of ZnSe grown on a GaAs substrate. In agreement with previous investigations, the Raman data can be described by taking into account Fröhlich and deformation potential interaction. The observed strong elastic scattering comes in resonance with the heavy- and light-hole exciton states and exhibits a pronounced angular dependence. The analysis in terms of a previously developed localized exciton model gives localization lengths of several wavelengths, suggesting a free exciton-polariton model to be more appropriate. This conclusion is further supported by our observation of oscillations in the measured cross-section that are quantitatively explained by exciton-polariton interferences.