Nature of coupled-mode contributions to hot-electron relaxation in semiconductors

The energy flow in a system of hot electrons, hot LO phonons, and a bath of acoustic phonons is studied using nonequilibrium Green functions. In lowest order, Kogan's formula for the energy-loss rate is obtained. When coupled modes are included we find, in sharp contrast to Das Sarma and co-workers, that the energy-loss rate is significantly suppressed by coupled-mode formation and quasiparticlelike modes do not contribute to the energy-loss rate.