  Field-effect transistors based on band-to-band tunneling (BTBT) have gained a
lot of recent interest due to their potential for reducing power dissipation in
integrated circuits. In this paper we present a detailed performance comparison
between conventional n-i-n MOSFET transistors, and BTBT transistors based on
the p-i-n geometry (p-i-n TFET), using semiconducting carbon nanotubes as the
model channel material. Quantum transport simulations are performed using the
nonequilibrium Green's function formalism including realistic phonon
scattering. We find that the TFET can indeed produce subthreshold swings below
the conventional MOSFET limit of 60mV/decade at room temperature leading to
smaller off-currents and standby power dissipation. Phonon assisted tunneling,
however, limits the off-state performance benefits that could have been
achieved otherwise. Under on-state conditions the drive current and the
intrinsic device delay of the TFET are mainly governed by the tunneling barrier
properties. On the other hand, the switching energy for the TFET is observed to
be fundamentally smaller than that for the MOSFET, reducing the dynamic power
dissipation. Aforementioned reasons make the p-i-n geometry well suited for low
power applications.
