Abstract
We have investigated relaxation dynamics of hot carriers and formation dynamics of excitons in an In 0.53Ga 0.47As thin film at 4.2 and 77 K by means of femtosecond pump and probe spectroscopy. The spectral change of exciton absorption band induced by the pumping pulse is composed of broadening and peak shift. The broadening is attributed to scattering of excitons created around the Γ point by the probe pulse with free carriers generated by the pumping pulse. The observed blue and red shifts are ascribed to the exciton–exciton exchange interaction and the band-gap renormalization, respectively. The time evolution of the shifts of the order of 30 ps is interpreted in terms of the energy-loss processes of hot carriers with emission of optical phonons. Comparison of the observed decay behaviors with the theoretical calculation, taking into account the Frohlich interaction, indicates a reduction in the carrier cooling rate by a factor of 40 in highly excited In 0.53Ga 0.47As.
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