DENSITY-DEPENDENCE OF THE EXCITON ENERGY IN SEMICONDUCTORS

We investigate both experimentally and theoretically the excitonic abs orption in ZnSe in a temperature range between 2 and 60 K with increas ing densities of carriers. For higher temperatures a weak redshift of the exciton resonance is found which turns into a blueshift for lower temperatures. While the widely used simplified treatment of the scatte ring processes within a static screening approximation fails completel y to describe this thermally induced crossover, it can be explained by the interplay between Coulomb-Hartree-Fock renormalizations and carri er-carrier and carrier-polarization scattering including the dynamical screening.