Abstract

Ultrafast hot-carrier energy relaxation in polar semiconductors, such as GaAs, has been investigated intensively for more than a decade. For carrier densities well above 10¹⁷cm⁻³, the energy loss rate is found to be strongly reduced and has been attributed to (a) generation of a high density of nonequilibrium LO phonons in a small region of Brillouin zone¹ or (b) screening of the Fröhlich interaction between electrons and LO phonons.² Theoretical explanations favor the former explanation but are complicated by many-body processes, such as the coupled plasmon- phonon modes, on energy relaxation. Experimentally, the contributions of phonon and carrier effects to the cooling rate are not easily separated by usual optical techniques since both effects scale with the excitation level or carrier density.

© 1993 Optical Society of America