Hot-Electron Recombination at Neutral Acceptors in GaAs: A cw Probe of Femtosecond Intervalley Scattering

The rates at which hot electrons scatter from the $\Gamma$ valley to the $L$ and $X$ valleys in GaAs have been measured as a function of electron energy. Scattering times are determined from the relative efficiency of recombination of hot electrons with neutral acceptors at low injected-carrier densities. Representative scattering times are ${\tau }_{\Gamma L}=540\mathrm{}\pm 120$ fsec for 0.48-eV electrons and ${\tau }_{\Gamma X}=180\mathrm{}\pm 40$ fsec for 0.58-eV electrons. Our results enable us to reconcile the large range of scattering rates reported in other experiments and demonstrate the power of this cw probe to study subpicosecond electron dynamics.