  We propose a model for partially ballistic MOSFETs and for channel
backscattering that is alternative to the well known Lundstrom model and is
more accurate from the point of view of the actual energy distribution of
carriers. The key point is that we do not use the concept of "virtual source".
Our model differs from the Lundstrom model in two assumptions: i) the
reflection coefficients from the top of the energy barrier to the drain and
from top of the barrier to the source are approximately equal (whereas in the
Lundstrom model the latter is zero), and ii) inelastic scattering is assumed
through a ratio of the average velocity of forward-going carriers to that of
backward-going carriers at the top of the barrier kv > 1 (=1 in the Lundstrom
model). We support our assumptions with 2D full band Monte Carlo (MC)
simulations including quantum corrections in nMOSFETs. We show that our model
allows to extract from the electrical characteristics a backscattering
coefficient very close to that obtained from the solution of the Boltzmann
transport equation, whereas the Lundstrom model overestimates backscattering by
up to 40%.
