SPECTRAL-HOLE BURNING AND CARRIER THERMALIZATION IN GAAS AT ROOM-TEMPERATURE

We report on femtosecond time-resolved transmission and reflectivity m easurements on bulk GaAs. Spectral-hole burning is observed, to our kn owledge, for the first time in GaAs at room temperature. Carrier therm alization occurs within 200 fs and shows no significant dependence on excitation density or excess energy in the range from 2 x 10(17) cm(-3 ) to 2 x 10(18) Cm-3 and 35 meV to 90 meV, respectively. Calculations of the carrier dynamics are performed and include full dynamic screeni ng of the carrier-carrier and the carrier LO-phonon interaction. The c alculated thermalization times agree well with the experimental result s. Negative transmission changes above the spectral hole are mainly ca used be and complementary increase of reflectivity, but not by an incr ease of absorption.