Ultrafast electron relaxation through Coulomb collisions in GaAs

We have used a nondegenerate pump-probe configuration allowing to isolate the electron dynamics in intrinsic GaAs. Nonequilibrium electron populations giving rise to spectral hole burning were observed for a wide range of densities and excess energies and their redistribution due to Coulomb collisions was studied. Surprisingly, the redistribution is slower at higher densities due to band-filling effects and to the ineffectiveness of screening at early times and for low densities.