Electron-phonon quantum kinetics in pulse-excited semiconductors: Memory and renormalization effects

The carrier dynamics in photoexcited semiconductors is studied in a quantum kinetic approach based on the density-matrix formalism. Besides the memory effects related to the energy-time uncertainty, we discuss interference effects between different types of interactions describing the fact that a transition due to one interaction occurs between states, which are renormalized by other interactions. We first analyze the relaxation process in a one-band model, which allows us to concentrate on memory effects in the electron-phonon interaction. We then extend the model to a two-band semiconductor interacting with a short laser pulse, which is more realistic due to the explicit treatment of the carrier generation process. Here we discuss, in particular, the role of renormalization effects. It turns out that these effects reduce the broadening due to the non-Markovian dynamics and lead to distribution functions, which are more similar to the semiclassical case; the positions of the peaks, however, exhibit slight time-dependent shifts. On the other hand, phonon quantum beats in the decay of the interband polarization are increased by these renormalization effects.