STRONG DEPHASING IN A LASER-EXCITED SEMICONDUCTOR DUE TO CARRIER-PLASMON SCATTERING

The generation of a dense electron-hole plasma by an intense short las er pulse is investigated by solving the semiconductor Bloch equations. The kinetics of plasmons on a sub-ps time scale is demonstrated to be important for the relaxation and dephasing behaviour in comparison to a simple static treatment of screening under the considered excitatio n conditions with carrier densities in the range of 10(17) to 10(18) c m(-3) for GaAs. Strong dephasing is found particularly for the early s tage of the excitation, when the pulse is rising. However, peak scatte ring with dephasing times below 10 fs as shown by Scott et al. [1] to be possible for strongly peaked nonequilibrium carrier distributions i s prevented by the fast relaxation of the excitation peak and the fast filling of carrier distributions at small wavenumbers. Scattering of the coherent polarization at the carriers reduces the decay of polariz ation in comparison with the dephasing-rate approximation, where it is generated by carrier-carrier scattering only. Moreover coherent scatt ering decreases the generation rate of carriers in the presence of the pulse resulting in a strongly reduced final carrier density.