Nonequilibrium electron-phonon scattering in semiconductor heterojunctions.

We calculate the energy loss rate of a quasi-2D hot-electron gas at a semiconductor heterojunction due to the emission and reabsorption of nonequilibrium optical phonons. A kinetic equation for the nonequilibrium lattice excitations (hot phonons) in the spatially inhomogeneous field created by the quasi-2D electrons is obtained. The equation is solved by a transformation that introduces the occupation number for wavepackets of phonons that are "localized" in a spatial region near the electron layers. Our result does not contain the spurious dependence on the size of the sample that results when the nonequilibrium phonons are represented in terms of decoupled 3D plane waves. We apply our results to electrons in a GaAs-Ga(x)Al(1-x)As heterojunction.