Quantum confinement and hot-phonon effects in quantum wells

Abstract

We present a theoretical study of the dynamics of photoexcited carriers in GaAs/GaAlAs quantum-well structures. Both the effects of lattice heating and of the energy exchange between electrons and holes on the carrier relaxation are included. The dynamics of the nonequilibrium optical phonons is described by a kinetic equation for phonon wave packets that properly incorporates the effect of carrier confinement on the nonthermal lattice modes. The modifications of the phonons due to the layered lattice structure are not considered here. For the carriers, Fermi–Dirac distribution functions are used and the electron–hole interaction is included explicitly. Results of this approach are presented for different layer thicknesses and are compared with the results of a previous calculation by one of us for bulk GaAs to assess the effect of quantum confinement on the carrier cooling. Confinement in quantum–well structures is found to increase the carrier cooling rate as compared to bulk GaAs. The cooling rate also increases as the well gets narrower, in agreement with recent experimental observations.