Hot electron luminescence in p-GaAs: A spectroscopic probe of femtosecond phenomena

Abstract

Optical studies of electron-scattering processes in GaAs often utilize ultrafast laser techniques to directly resolve the femtosecond scattering times. The author has achieved comparable time resolution with CW (continuous wave) or picosecond lasers, using the 200-fs LO (longitudinal optic) phonon emission time as an internal clock against which other scattering processes can be measured. The recombination of optically injected hot electrons at neutral acceptors in lightly p-type GaAs (p< 2 × 1017 cm-1) is measured with a CW detector, varying the laser photon energy of the injected carrier density. At low injected carrier densities, this luminescence shows an oscillatory structure with peaks separated by the 37-MeV LO phonon energy. Straightforward analysis of this luminescence as a function of the laser photon energy gives the intervalley scattering time as a function of electron energy. The energy-loss rate of a hot electron to a cool electron-hole plasma has been determined by comparing the hot acceptor luminescence in the presence of the plasma with that in the absence of the plasma.