This work deals with the dynamics of the nonthermalized electron-hole plasma in the subpicosecond regime. We computed different collision rates (electron-electron, electron-hole, electron-phonon) and discussed the relative efficiency of the different processes for the cases of static and dynamic screening of the interaction. We also considered how the inclusion of the exchange affected the screening amplitude and the collision rates. Calculations were bases upon GaAs. We conclude that dynamic screening is crucial for electrons in the conduction band at high plasma density [say, at densities above (1-2)x10 16 /cm 3 ] whereas it generally plays a minor role at low density and when describing hole dynamics. The excitation of heavy holes into the light-hole band by collisions with the conduction electrons is discussed in heavily p-doped GaAs.

We report on femtosecond time-resolved transmission and reflectivity measurements on bulk GaAs. Spectral-hole burning is observed, to our knowledge, for the first time in GaAs at room temperature. Carrier thermalization occurs within 200 fs and shows no significant dependence on excitation density or excess energy in the range from 2 x 10 cm to 2 x 10 cm and 35 meV to 90 meV, respectively. Calculations of the carrier dynamics are performed and include full dynamic screening of the carrier-carrier and the carrier LO-phonon interaction. The calculated thermalization times agree well with the experimental results. Negative transmission changes above the spectral hole are mainly caused by a complementary increase of reflectivity, but not by an increase of absorption.

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