Single wall carbon nanotube field effect transistor model

The low-energy-limit band structure of carbon nanotubes (CNTs) indicates parabolic behavior. However it is not parabolic in other parts of the band energy. Based on the confinement effect we present an analytical model that captures the essence of the physical processes in a carbon nanotube field effect transistor (CNTFET). The model covers seamlessly the whole range of transport from drift-diffusion to ballistic. It has been clarified that the intrinsic speed of CNTs is governed by the transit time of electrons. Although the transit time is more dependent on the saturation velocity than on the weak-field mobility, the feature of high-electron mobility is beneficial in the sense that the drift velocity is always maintained closer to the saturation velocity, at least at the drain end of the transistor where electric field is necessarily high and controls the saturation current. The results obtained are applied to the modeling of the current-voltage characteristics of a CNTFET. The channel-length modulation is shown to arise from the drain velocity becoming closer to the ultimate saturation velocity as the drain voltage is increased