A comprehensive study of ultrafast carrier dynamics of LT-GaAs: Above and below bandgap regions

We report the study of ultrafast carrier dynamics of low temperature grown GaAs over wide spectral range (2.75 eV-0.88 eV) with above and below bandgap (E-g) optical excitations using ultrafast transient absorption spectroscopy. The presence of defects and their subsequent effect on the pathway and lifetime of carrier relaxation with probing at different energy levels is presented. The carrier relaxation pathways and their corresponding models are predicted. It is observed that for pumping (2.58 eV) and probing above Eg, the transient behavior is dominated by band filling while renormalization is in prominence when probed near to E-g. For below Eg pumping (0.88 eV) the optical behavior is mostly governed by defects. The calculated trap time is in the range of -128 fs to -807 fs while overall recombination time shows a wide variation from -1.38 ps to -1.25 ns depending on the position of traps/defects in the forbidden band.