HOT-CARRIER DYNAMICS NEAR THE FERMI-EDGE OF N-DOPED GAAS

Femtosecond bleaching measurements are performed in n-doped GaAs at bo th 300 K and 14 K using low densities of carriers injected at 2 eV. Th e dwell time of electrons excited far above the Fermi sea is reduced b ecause of hot-electron/cold-electron interactions. The response at 14 K is much stronger and slower than that at 300 K. This is attributed t o: (i) the proximity to the Fermi level of the conduction band states probed via split-off valence band coupling; (ii) slow Landau damping o f non-equilibrium plasmons, primarily by the minority holes which then heat the majority electrons.