TIME-RESOLVED RAMAN MEASUREMENT OF INTERVALLEY SCATTERING IN GASB

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