A quantum description of drift velocity overshoot at high electric fields in semiconductors

A quantum description of transient charge transport in semiconductors is presented. In particular, we discuss the drift velocity overshoot in GaAs. The paper is intended to show how typical quantum features, such as intracollisional field effect and multiple collisions tend to modify the transient behavior of the system as predicted by semiclassical transport. This analysis has been performed by means of a quantum Monte Carlo procedure which takes into account the GaAs band structure through a many-valley model. The results of the quantum simulation, as regards drift velocity and upper valley population, have been compared with those of the classical theory and this comparison shows that in the case of GaAs quantum features are not relevant. For a better understanding, a semiconductor model, characterized by a very strong electron-phonon coupling constant, has been considered where quantum effects are appreciable and from this analysis it is possible to identify physical systems for which a full quantum treatment is required.