Ultrafast relaxation of photoexcited carriers: The role of coherence in the generation process

A self-consistent description of the ultrafast dynamics of photoexcited carriers in semiconductors based on a generalized Monte Carlo solution of the semiconductor Bloch equations is presented. The problem of photogeneration and its theoretical description are discussed. We show that some of the approaches commonly used fail in describing correctly the effect of carrier-carrier interaction in the low-density limit. By including terms which have the structure of ‘‘in-scattering’’ terms (vertex corrections) for the interband polarization, the experimentally observed features in the carrier dynamics are well described in the whole density range.