SUBBAND GAP CARRIER DYNAMICS IN LOW-TEMPERATURE-GROWN GAAS

Measurements of the carrier relaxation dynamics in low-temperature-gro wn GaAs have been made with a femtosecond-resolution, time-resolved pu mp-probe technique using a subband-gap probe-beam wavelength. The tran sient absorption and index of refraction changes have been analyzed us ing a relaxation model with up to four different excited state populat ions. The carrier recombination time within the midgap trap states is found to be longer than the subpicosecond free-carrier trapping time. Two time scales are observed for the recombination rate, one of a few picoseconds and one of hundreds of picoseconds, indicating the presenc e of at least two different trap states for the free-carriers in this material. (C) 1997 American Institute of Physics.