  Ideal, completely coherent quantum transport calculations had predicted that
superlattice MOSFETs may offer steep subthreshold swing performance below
60mV/dec to around 39mV/dec. However, the high carrier density in the
superlattice source suggest that scattering may significantly degrade the ideal
device performance. Such effects of electron scattering and decoherence in the
contacts of superlattice MOSFETs are examined through a multiscale quantum
transport model developed in NEMO5. This model couples NEGF-based quantum
ballistic transport in the channel to a quantum mechanical density of states
dominated reservoir, which is thermalized through strong scattering with local
quasi-Fermi levels determined by drift-diffusion transport. The simulations
show that scattering increases the electron transmission in the nominally
forbidden minigap therefore degrading the subthreshold swing (S.S.) and the
ON/OFF DC current ratio. This degradation varies with both the scattering rate
and the length of the scattering dominated regions. Different superlattice
MOSFET designs are explored to mitigate the effects of such deleterious
scattering. Specifically, shortening the spacer region between the superlattice
and the channel from 3.5 nm to 0 nm improves the simulated S.S. from 51mV/dec.
to 40mV/dec. I. INTRODUCTION
