GREENS-FUNCTION DESCRIPTION OF MOMENTUM-ORIENTATION RELAXATION OF PHOTOEXCITED ELECTRON PLASMAS IN SEMICONDUCTORS

We present numerical results for the momentum-orientation relaxation o f optically excited electron plasmas in bulk semiconductors. Our resul ts are based on the full two-time Green's function approach for carrie r-carrier scattering and are compared to the results obtained within t he conventional quantum Boltzmann equation. Defining ''memory effects' ' by this comparison, we find memory effects mainly to be differences in the time-scale of the relaxation process rather than distinct quali tative features. Within the limitations of our isotropic static screen ing model, we find that, in both approaches, an initial anisotropic an d nonmonotonic distribution function relaxes in a three-stage process in which the distribution becomes monotonic before it loses its anisot ropy.