Nonequilibrium phonon effect on time-dependent relaxation of hot electrons in semiconductor heterojunctions

We have studied the effect of a nonequilibrium population of optical phonons on the energy relaxation of two-dimensional (2D) hot electrons in a semiconductor quantum well. A time-dependent analysis of the coupled electron--LO-phonon system is presented. The 2D electrons are described by a temperature Tₑ(t). The dynamics of the nonequilibrium lattice excitations is governed by a kinetic equation for ``phonon wave packets'' that was derived recently by us. If the lifetime of the LO phonons is larger than 5 psec, phonon reabsorption can slow down considerably the carrier cooling. The time evolution of the carrier temperature is calculated. The comparison with recent experiments is discussed.