Initial thermalization of photoexcited carriers in GaAs studied by femtosecond luminescence spectroscopy

Relaxation of a nonequilibrium distribution of electrons and holes in GaAs following femtosecond photoexcitation is investigated via spectrally and time-resolved luminescence. A rapid onset of luminescence over a broad spectral range shows that both electrons and holes are redistributed over a wide energy range within 100 fs, even at excitation densities as low as ${10}^{17}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. The data demonstrate carrier-carrier scattering rates higher than predicted by calculations with a statically screened interaction potential. Monte Carlo simulations using dynamical screening account for the experimental results.