PHOTOLUMINESCENCE FROM HOT CARRIERS IN LOW-TEMPERATURE-GROWN GALLIUM-ARSENIDE

Band-to-band photoluminescence spectra of GaAs grown at 200-degrees-C by molecular beam epitaxy have been measured as a function of lattice temperature (10 < T(L) < 290 K), laser photon energy (1.62 < E(p) < 2.07 eV) and excitation intensity during 5 ps excitation. Carrier recombination, previously reported to be as fast as 300 fs in this material, displays at most a weak density dependence, consistent with a monomolecular mechanism. The spectra correspond to quasi-steady-state carrier distributions which evolve from nonthermal to thermal character as the density increases from 10(16) to 10(18) cm-3. For the thermal distributions, the characteristic temperature depends strongly on E(p); values near 1000 K are obtained for E(p) > 1.85 eV. The results are related to ultrafast carrier recombination, intervalley transfer, and thermalization.