Band-structure effects on the femtosecond energy relaxation of photoexcited electrons in ${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As/GaAs quantum wells

Results of Monte Carlo simulations of the femtosecond relaxation of electrons in an ${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As/GaAs quantum well excited by a 2-eV laser are presented. Mixing of light- and heavy-hole subbands results in an initial photoexcited electron distribution much broader in energy than in bulk GaAs. Comparison with experiments [M. Rosker, F. Wise, and C. L. Tang, Appl. Phys. Lett. 49, 1714 (1986)] shows that the previously unexplained lack of a 160-s relaxation component in the quantum well, observed in bulk GaAs and attributed to polar-optical-phonon (POP) scattering, can be accounted for by this broad distribtuion and is not associated with an absence of POP scattering.