Effect of annealing on the nonequilibrium carrier lifetime in GaAs grown at low temperatures

GaAs samples grown by molecular-beam epitaxy at low (230$^\circ$C) temperatures are investigated. One of the samples is subjected to aftergrowth annealing at 600$^\circ$C. Using an unconventional pump-probe scheme for measuring the dynamic variation in the light refractive index, the nonequilibrium charge-carrier lifetime (275 $\pm$ 30 fs before annealing) is determined. Such a short carrier lifetime in the unannealed material is due to the high concentration of point defects, mainly AsGa antisite defects. According to X-ray diffraction and steady-state optical absorption data, the AsGa concentration in the samples is 3 $\times$ 10$^{19}$ cm$^{-3}$, which corresponds to an arsenic excess of 0.26 at%. Upon annealing at 600$^\circ$C, the superstoichiometric As defects self-organize and form As nanoinclusions in the GaAs crystal matrix. It is shown that in this case the nonequilibrium charge-carrier lifetime increases to 452 $\pm$ 5 fs. This lifetime is apparently ensured by the capture of non-equilibrium charge carriers at metal As nanoinclusions.