Electron-electron scattering modifications of intervalley transition rates and ultrafast relaxation of hot 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, to probe various scattering mechanisms and the dynamic screening of hot carriers in semiconductors. 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 lifetime decreases with increasing density. This decrease agrees both in lifetime magnitude and in density dependence with recent experimental measurements. The presence of electron-electron scattering modifies both the population transition rates and the carrier densities in the satellite valleys, primarily by reshaping the energy distribution of carriers in the central valley. Intervalley scattering rates slow by two orders of magnitude as the electronic system cools in the first picosecond. Thus, while intervalley processes do play a role in the initial decay, the same processes play a 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.