Experimental Evidence for Optical Population of theXMinima in GaAs

Electrons photoexcited in $p^{++}$-GaAs (with Cs surface monolayer) are found to "thermalize" in either the $\Gamma$ or $X$ conduction-band minima while diffusing to the surface. Two strong peaks separated by 0.3 eV of photoemitted electrons associated with these minima are observed in the energy distribution curves for $1.5 \mathrm{eV}<~h\nu <~3.2 \mathrm{eV}$.