Femtosecond Spectroscopy of Non-thermal Carrier Distributions in GaAs Quantum Wells

Our understanding of elementary carrier scattering processes in semiconductors on the femtosecond timescale has advanced remarkably in the past few years. Improvements in femtosecond optical pulse generation and detection techniques have allowed us to probe on shorter timescales with better sensitivity at carrier densities where complicated many-body interactions are manifest. We describe experiments in which non-thermal distributions of carriers are excited and studied in GaAs quantum wells. By modulation-doping, we introduce excess carrier populations which are thermalized to the lattice and study the effects of excess populations of electrons and holes alternately on the femtosecond thermalization. We obtain information on the effects of excess populations on inelastic carrier-carrier scattering rates, bandgap renormalization and electron-phonon coupling.