Influence of electron-hole scattering on subpicosecond carrier relaxation in AlxGa1-xAsGaAs quantum wells

We have simulated subpicosecond-time-scale pump-and-probe absorption experiments in AlxGa1-xAsGaAs quantum wells using an ensemble Monte Carlo calculation of the photoexcited electron-hole system. For excess carrier energies less than the optical-phonon energy, our results show that the apparent 200-fs relaxation observed in differential transmission experiments is directly attributable to relaxation of electrons through electron-electron scattering with inelastic electron-hole scattering playing a smaller role. Photoexcited holes are found to thermalize on a 50-fs time scale which is much shorter than the relaxation time of the electrons. However, a non-thermal hole distribution develops after the pulse due to optical-phonon absorption at 300 K which should give rise to absorption features at higher photon energies.