ULTRAFAST ELECTRON RELAXATION THROUGH COULOMB COLLISIONS IN GAAS

We have used a nondegenerate pump-probe configuration allowing to isol ate the electron dynamics in intrinsic GaAs. Nonequilibrium electron p opulations giving rise to spectral hole burning were observed for a wi de range of densities-and excess energies and their redistribution due to Coulomb collisions was studied. Surprisingly, the redistribution i s slower at higher densities due to band-filling effects and to the in effectiveness of screening at early times and for low densities.