Transport analysis of the thermalization and energy relaxation of photoexcited hot electrons in Ge-doped GaAs

A very fast broadening, thermalization, and cooling of an initially narrow photoexcited electron distribution was recently observed in the time- and frequency-resolved electron-acceptor luminescence of p-type bulk GaAs:Ge for near-band-gap excitation at low excitation densities and temperatures. As the short thermalization times could not be explained by the standard rates for the conventional carrier-carrier, carrier-impurity, and carrier-phonon scatterings, unconventional types of thermalizing carrier interactions were originally suggested to interpret the data. In contrast, the present analysis restricts itself to the conventional scattering mechanisms, but attempts to explain the fast thermalization and cooling rates by accounting for the finite experimental pulse-repetition rates and the resulting presence of neutral donors of the amphoteric germanium, causing a very effective additional electronic energy-relaxation channel via impact ionizations of Ge donors. {} 1996 The American Physical Society.