Simulation of phonon-assisted band-to-band tunneling in carbon nanotube field-effect transistors

Electronic transport in a carbon nanotube metal-oxide-semiconductor field effect transistor (MOSFET) is simulated using the nonequilibrium Green's functions method with the account of electron-phonon scattering. For MOSFETs, ambipolar conduction is explained via phonon-assisted band-to-band (Landau-Zener) tunneling. In comparison to the ballistic case, we show that the phonon scattering shifts the onset of ambipolar conduction to more positive gate voltage (thereby increasing the off current). It is found that the subthreshold swing in ambipolar conduction can be made as steep as 40 mV/decade despite the effect of phonon scattering.