DIRECT MEASUREMENTS OF MANY-BODY EFFECTS ON FREE-CARRIER - LO-PHONON INTERACTIONS IN GAAS QUANTUM-WELLS

The influence of electron-hole pairs on free-carrier-LO-phonon interac tions in GaAs quantum wells has been studied from the lattice perspect ive using a visible laser and Raman scattering to monitor LO-phonon dy namics following hot-carrier injection and relaxation. The LO-phonon d ynamics were systematically studied as the density of a cold free-carr ier population was controlled using an infrared laser. The lifetime of small-wave-vector LO phonons decreases from 4.5 to 1.9 ps as the cold carrier density increases to approximately 3 x 10(11) cm-2, and there is a corresponding reduction in their nonequilibrium occupation numbe r. These results provide direct evidence of hot-phonon reabsorption an d a reduction in the cooling rate from the hot-carrier-LO-phonon syste m to the lattice bath.