TIME-RESOLVED RAMAN MEASUREMENT OF INTERVALLEY SCATTERING IN GASB

Time-resolved Raman spectroscopy with subpicosecond resolution has been used to measure L-GAMMA intervalley scattering of photoexcited electrons in GaSb. Our experiment measures directly the time-dependent occupancy of non-equilibrium longitudinal optic phonons with wavevector approximately 10(6) cm-1 which are generated by intra-GAMMA relaxation of electrons near the GAMMA minimum. The phonon population shows a two-component decay: at times less than or similar to 10 ps, phonons are generated by direct electron relaxation within the GAMMA valley, and their decay is due to anharmonicity and reabsorption. At later times the phonon decay rate slows, as L-GAMMA intervalley scattering heats electrons at GAMMA. At low temperature the intervalley relaxation time is measured to be 54 ps, corresponding to an effective intervalley deformation potential D(GAMMAL) = 3.2 eV angstrom-1.