Femtosecond absorption saturation studies of hot carriers in GaAs and AlGaAs

Femtosecond carrier dynamics in GaAs and AlGaAs thin films are studied by time-resolved pump-probe spectroscopy. Measurements are performed using identical pulses as well as a continuum probe. Observations of the ultrafast absorption saturation response are related to the excitation of the carriers into specific nonthermal distributions, to their rapid scattering out of these states, and to subsequent cooling of the quasi-thermal carrier distribution to the temperature of the lattice. A strong dependence of the initial scattering rates on the mole fraction of Al and the excess electron energy is observed.<>