Analytical Model of Nanowire FETs in a Partially Ballistic or Dissipative Transport Regime

The intermediate transport regime in nanoscale transistors between the fully ballistic case and the quasi-equilibrium case, described by the drift-diffusion (DD) model, is still an open modeling issue. Analytical approaches to the problem have been proposed, based on the introduction of a backscattering coefficient, or numerical approaches consisting in the Monte Carlo solution of the Boltzmann transport equation or in the introduction of dissipation in quantum transport descriptions. In this paper, we propose a simple analytical model to seamlessly cover the whole range of transport regimes in generic quasi-1-D field-effect transistors, and apply it to silicon nanowire transistors. The model is based on describing a generic transistor as a chain of ballistic nanowire transistors in series, or as the series of a ballistic transistor and a DD transistor operating in the triode region. As an additional result, we find a relation between the mobility and the mean free path that has deep consequences on the understanding of transport in nanoscale devices.