Abstract
The paper presents a Monte Carlo study of ultrafast phenomena in polar semiconductors. The main focus is given to the analysis of cooling of carriers following subpicosecond laser excitations in GaAs and InP. Excellent agreement is found with time-resolved photoluminescence data. A strong non-equilibrium LO phonon population is found, which at high densities and low temperatures slows down the cooling of the photoexcited carriers. The role of upper valleys in the cooling process is crucial and explains the different behavior found in GaAs versus InP. A discussion of experimentally determined effective temperatures is given.