QUASI-CLASSICAL APPROXIMATION AND DYNAMIC RENORMALIZATIONS OF THE ENERGY-BANDS IN HIGHLY EXCITED BULK SEMICONDUCTORS

The quasiclassical approximation for degenerate fermion systems that uses momentum-integrated nonequilibrium Green's functions is introduced into the theory of highly excited semiconductors. As an example, the complex density-dependent retarded self-energies and the spectral functions are evaluated analytically for a thermal electron-hole plasma. Furthermore, the renormalizations of the bands are calculated. The resulting band shrinkage extends in momentum space only between one and two Fermi wave numbers around the band extrema. The quasiclassical approach particularly emphasizes dynamical correlations that are neglected in the conventional quasistatic and quasiparticle approximations. It is a valuable method, if dynamical effects are important, as, for example, in line-shape theories.