  Band-to-band tunneling (BTBT) devices have recently gained a lot of interest
due to their potential for reducing power dissipation in integrated circuits.
We have performed extensive simulations for the BTBT operation of carbon
nanotube metal-oxide-semiconductor field-effect transistors (CNT-MOSFETs) using
the non-equilibrium Green's functions formalism for both ballistic and
dissipative quantum transport. In comparison with recently reported
experimental data (Y. Lu et al, J. Am. Chem. Soc., v. 128, p. 3518-3519, 2006),
we have obtained strong evidence that BTBT in CNT-MOSFETs is dominated by
optical phonon assisted inelastic transport, which can have important
implications on the transistor characteristics. It is shown that under large
biasing conditions two-phonon scattering may also become important.
