MULTIPHONON RELAXATION OF ELECTRONS IN A SEMICONDUCTOR QUANTUM-DOT

Intra-band electron relaxation via phonon emission is an important process that governs the light emission efficiency of semiconductor lasers. Using a perturbation theory, electron relaxation rate in a GaAs quantum dot is calculated to the second order in electron-phonon interactions. If first order processes only are included, rapid relaxation in a small (< 1000 angstrom) dot is impossible unless the interlevel separation is exactly tuned to the LO phonon energy. Two-phonon (LO +/- LA) processes significantly alleviate the tuning condition by creating a window of rapid (subnanosecond) relaxation around the LO phonon energy. Based on this finding, prescriptions are given for the achievement of highly-efficient quantum dot lasers.