Abstract
Time-resolved luminescence and Raman measurements have indicated in recent years the existence of nonequilibrium phonon distributions, as a result of the cooling of phototexcited electrons and holes in GaAs. While several analytic studies of hot phonons have appeared in the literature, we present here a novel Ensemble Monte Carlo calculation of nonequilibrium-phonon effects on the relaxation rate of photoexcited electrons. The build up of the phonon population on a picosecond scale is monitored, in parallel with the cooling of the electron distribution. No assumptions on the form of the phonon or the electron distributions are required. The strong phonon emission by the high-energy photoexcited electrons in the first stage of their relaxation (within a few tenths of a picosecond) is found to drive the phonon distribution strongly out of equilibrium. After the excitation, reabsorption of the emitted phonons by the carriers and nonelectronic phonon decay processes bring the distribution back to its equilibrium value. The time evolution of the calculated phonon distribution is in agreement with the available data obtained with time-resolved Raman spectroscopy. Moreover, the strongly perturbed phonon distribution can, for the moderate carrier excitation densities considered, fully account for the observed reduction of the cooling rate of the phototexcited carriers. Finally the arguments for and against a dominant role of free carrier screening are critically analysed in the light of the present and of foregoing theoretical hot-phonon theories.