Simulation of Electronic Transport in Carbon Nanotube Field Effect Transistors

In recent years, Carbon nanotube (CN) field effect transistors (CNFETs) with a sub-threshold slope of 40mV/dec have been demonstrated, which is less than the thermal limit of 60mV/dec\footnote{Appenzeller, J., \emph{et al.}, \emph{IEEE Trans. Elec. Dev.}, \textbf{52}, 2568, (2005)}. By exploiting inter-band tunneling, the transmission ratio comes to depend on the density of states rather than the thermal distribution of carriers in the contacts. Using tight-binding approximations to the Hamiltonian in the Keldysh non-equilibrium Green's function (NEGF) formalism, we study the transport properties of CNFETs under a tunneling mode bias. Phonon coupling effects are included through the self-consistent Born approximation (SCBA). The mode-space approach to decoupling the Hamiltonian\footnote{Venugopal, R., \emph{et al.}, \emph{J. Appl. Phys., }\textbf{92}, 3730, (2002)} is extended to include chiral nanotubes, such that a more realistic class of CNs may be treated with computational efficiency. Further, a comparison is made between the $\pi$-orbital and $\pi+\sigma$-orbital tight-binding models. Here, we find that transport is minimally affected. The geometry and electrostatic contact doping are examined to optimize device performance.