Comparison of optical pump-probe characterization of low-temperature-grownGaAs at well-above-bandgap and near-bandedge wavelengths

Annealed low-temperature-grown GaAs was studied by time-resolved photorefle ctance measurement at well-above-bandgap photon energies and by photoreflec tance as well as transmission measurements at near-bandedge wavelength. At near-bandedge wavelength, the initial changes in reflectivity and transmiss ion were observed to relax at identical relaxation rate, which was attribut ed to the absence of carrier cooling and the domination of carrier trapping . All the measured photoreflectance traces were found to be well fitted by the previously proposed three-component decomposition procedure. Among the three components, the fast positive peak was attributed to absorption bleac hing and its relaxation, that is, the scattering of the photo-carrier out o f their initially excited states by carrier cooling and trapping. The decay times of the positive peak, combined with the carrier cooling times extrac ted from photoreflectance measurement on semi-insulating GaAs, give consist ent estimate of carrier trapping time at all wavelengths within the spectra l range. Our results verify that well-above-bandgap photoreflectance measur ement combined with the three-component fitting procedure can be used to es timate the photo-carrier trapping time which are consistent with that obtai ned by near-bandedge photoreflectance and transmission techniques.