Ultrafast electron-phonon scattering in semiconductors studied by nondegenerate four-wave mixing

Abstract

Nondegenerate four-wave-mixing allows one to monitor the femtosecond relaxation of free carriers in GaAs and CdTe at densities as low as $2\ifmmode\times\else\texttimes\fi{}{10}^{15}$ ${\mathrm{cm}}^{\ensuremath{-}3}.$ The energy relaxation time of electrons via LO-phonon emission is determined to be $240\ifmmode\pm\else\textpm\fi{}20$ fs in GaAs. In more polar CdTe, this time constant is found to be as short as $70\ifmmode\pm\else\textpm\fi{}15$ fs which is even shorter than the phonon oscillation period of 200 fs.