Quasi-ballistic, nonequilibrium electron distribution in inhomogeneous semiconductor structures

We report on a study of quasi-ballistic transport in deep submicron, inhomogeneous semiconductor structures, focusing on the analysis of signatures found in the full nonequilibrium electron distribution. We perform self-consistent numerical calculations of the Poisson-Boltzmann equations for a model n(+)-n(-)-n(+) GaAs structure and realistic, energy-dependent scattering. We show that, in general, the electron distribution displays significant, temperature dependent broadening and pronounced structure in the high-velocity tail of the distribution. The observed characteristics have a strong spatial dependence, related to the energy-dependence of the scattering, and the large inhomogeneous electric field variations in these systems. We show that in this quasi-ballistic regime, the high-velocity tail structure is due to pure ballistic transport, whereas the strong broadening is due to electron scattering within the channel, and at the source(drain) interfaces.