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 thermalization and relaxation of optically excited electrons and holes in intrinsic and p-type bulk GaAs and InP is presented. Using 50-fs and 2-eV laser-excitation pulses the hot-carrier dynamics was studied by the transient-absorption changes at 2 eV and by time-resolved luminescence spectroscopy, with a time resolution of 50-80 fs. The materials and doping levels were chosen to obtain, in combination with extensive ensemble Monte Carlo simulations, detailed information on intervalley and interband transfers of electrons and holes and on the effects of nonequilibrium optic phonons, of ionizing carrier-neutral-acceptor scatterings, and of dynamical screening of the various carrier-carrier interactions. Very good agreement between theory and experiment is found for the transient-absorption bleachings and the band-gap luminescence as functions 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.