Effect of electron-electron scattering on intervalley transition rates of photoexcited carriers in GaAs

Abstract

The femtosecond relaxation of photoexcited carriers in GaAs is investigated by the use of ensemble Monte Carlo calculations coupled with a molecular-dynamics approach for the carrier-carrier interaction. The interaction of various scattering mechanisms and the dynamic screening of hot carriers in semiconductors is probed. At a density for which the GaAs is degenerate (in equilibrium), scattering out of the excitation volume is dominated in the initial tens of femtoseconds by electron-electron scattering, and the scattering rate increases with increasing density. This rate increase agrees both in magnitude and in its density dependence with recent experimental measurements. The presence of electron-electron scattering modifies both the population transition rates and carrier densities in the satellite valleys, primarily by reshaping the energy distribution of carriers in the central valley. Intervalley scattering rates decrease by 2 orders of magnitude as the electronic system cools during the first picosecond. Thus, intervalley processes do play a role in the initial decay and the same processes play a modified role in the picosecond-scale luminescence decay. We find that rates, for particular mechanisms of carrier transfer to the satellite valleys, must be estimated carefully since the Γ-L population shift contains a significant fraction of electrons that reach the L valleys by way of the X valleys.