Crossover from diffusive to quasi-ballistic transport

TLDR: In this article, a detailed study of quasi-ballistic transport in submicron semiconductor channels is presented, where the electron distribution in such channels differs significantly from a near-equilibrium, shifted Maxwell-Boltzmann distribution function, and displays a large broadening, as well as pronounced features, peaks and shoulders, in the high-velocity tail of the distribution associated with the nonequilibrium and quasiballistic nature of the electron transport.

Abstract: We present a detailed study of quasi-ballistic transport in submicron semiconductor channels. The electron distribution in such channels differs significantly from a near-equilibrium, shifted Maxwell-Boltzmann distribution function, and displays a large broadening, as well as pronounced features, peaks and shoulders, in the high-velocity tail of the distribution associated with the nonequilibrium and quasi-ballistic nature of the electron transport. For submicron channel lengths, analyses of the spatial dependence of the velocity distribution function show that scattering in the entire channel is important and that the scattering efficiency has a strong spatial dependence. In this article, we particularly study the crossover between the diffusive and quasi-ballistic regimes of transport and find characteristic signatures in (i) the electrostatics, which manifests as a redistribution of the voltage drop from the channel to the contact regions; (ii) the electron density, where exponential and linear spatial dependences of the source-injected and channel- and drain-backscattered electron densities are signatures of diffusive and quasi-ballistic transport, respectively, and (iii) the electron distribution function, where the source-injected ballistic peak observed in the quasi-ballistic regime disappears at the onset of diffusive transport.