Evolution of a nonthermal electron energy distribution in GaAs.

We have observed the thermalization of conduction electrons in GaAs from a nonthermal to a Maxwell-Boltzmann kinetic-energy distribution. A streak camera is used to observe the time-resolved spectrum of the band-to-acceptor luminescence following a short (5-ps) near-resonant laser pulse of very low excitation power. At electron density less than 10 14 cm -3 the thermalization of the electron energy distribution occurs with a rate independent of density on a time scale of 50 ps. Inelastic electron-phonon scattering is too slow to produce this thermalization