The roles of the electron-hole (e-h), electron-electron (e-e), hole-hole (h-h), and screened electron-phonon (e-ph) interactions on the ultrafast relaxation of photoexcited carriers in GaAs are examined. Theoretical expressions for the various scattering rates are obtained, and these are used in an ensemble Monte Carlo calculation. At low carrier concentrations the e-ph interaction is the main energy-loss channel for hot electrons, while at high carrier concentrations the e-h interaction is the primary energy-loss channel. This latter result follows from the high e-h scattering rate, the screening of the e-ph interaction, and the high efficiency of hole-phonon scattering through the unscreened deformation-potential interaction. The electron energy-loss rates through the e-h interaction increase as the excitation energies and intensities are increased. For excitation by an excess photon energy of 130 meV, for example, it is found that the e-e interaction slows the cooling rates at all excitation levels, while the h-h interaction enhances the cooling rate of the holes.

• Received 24 April 1987

DOI:https://doi.org/10.1103/PhysRevB.36.6018