Dynamics of nonthermal-carrier distributions in gaas generated by femtosecond laser pulses

We have studied hot electron to neutral acceptor recombination luminescence in p-type GaAs held at liquid-helium temperature. We are able to inject a moderate density (10¹⁵ cm^-3 to 10¹⁷ cm^-3) of carriers into the sample using femtosecond laser pulses. Two excitation energies are studied, 1.7 eV and 1.97 eV. At both energies the unrelaxed peak, due to electrons recombining with neutral acceptors before scattering, is attenuated considerably at higher carrier densities. The experimental data indicate that rapid carrier-carrier scattering within the highly nonequilibrium injected distribution occurs in the first 150 fs at carrier densities as low as 8 · 10¹⁵ cm^-3.