Effects of bandgap shrinkage in femtosecond absorption saturation measurements of GaAs film

Using CPM dye laser and self-mode-locked Ti sapphire laser as pump-probe optical sources, the effects of bandfilling and bandgap shrinkage on the femtosecond absorption saturation spectra of GaAs film have been studied. For exciting photon energy of 1.97 eV and carrier density of 1 × 1018 cm-3, an optical-induced absorption increase is observed and is attributed to bandgap shrinkage. The dependence of the absorption coefficient change on the carrier temperature and the carrier densities is discussed.