SUBPICOSECOND THERMALIZATION AND RELAXATION OF HIGHLY PHOTOEXCITED ELECTRONS AND HOLES IN INTRINSIC AND P-TYPE GAAS AND INP

A combined experimental and theoretical investigation of the thermaliz ation and relaxation of optically excited electrons and holes in intri nsic and p-type bulk GaAs and InP is presented. Using 50-fs and 2-eV l aser-excitation pulses the hot-carrier dynamics was studied by the tra nsient-absorption changes at 2 eV and by time-resolved luminescence sp ectroscopy, with a time resolution of 50-80 fs. The materials and dopi ng levels were chosen to obtain, in combination with extensive ensembl e Monte Carlo simulations, detailed information on intervalley and int erband transfers of electrons and holes and on the effects of nonequil ibrium optic phonons, of ionizing carrier-neutral-acceptor scatterings , and of dynamical screening of the various carrier-carrier interactio ns. Very good agreement between theory and experiment is found for the transient-absorption bleachings and the band-gap luminescence as func tions of time and doping. For times beyond 500 fs the effective plasma -temperatures T(eff), defined from the measured luminescence spectra, are well reproduced by theory. For shorter times, the calculated T(eff ) are systematically too high. This deviation is tentatively ascribed to effects of collisional broadening and band nonparabolicities.