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 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, T(e)(t). The dynamics of the nonequilibrium lattice excitations is governed by a kinetic equation for "phonon wavepackets" 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.