On the Interpretation of Local Negative Mobilities in Nanoscale Semiconductor Devices

In a previous theoretical work, the concept of mobility has been unequivocally extended to inhomogeneous nonequilibrium systems. This generalization naturally suggests a new one-particle Monte Carlo method to solve the Boltzmann equation, which can self-consistently take into account generation-recombination processes, as well as quantum corrections. This new scheme has been successfully applied to different kinds of MOSFETs. The results of the simulations clearly show that, surprisingly, the mobility in the channel can become negative. In this brief, we present a detailed analysis of this phenomenon and show that negative mobilities are directly related to regions, where quasi-ballistic transport takes place.