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Due to carrier band-to-band-tunneling (BTBT) through channel-source/drain contacts, conventional MOS-like Carbon Nanotube Field Effect Transistors (C-CNFETs) suffer from ambipolar conductance, which deteriorates the device performance greatly. In order to reduce such ambipolar behavior, a novel device structure based on electrostatic doping is proposed and all kinds of source/drain contacting conditions are considered in this paper. The non-equilibrium Green's function (NEGF) formalism based simulation results show that, with proper choice of tuning voltage, such electrostatic doping strategy can not only reduce the ambipolar conductance but also improve the sub-threshold performance, even with source/drain contacts being of Schottky type. And these are both quite desirable in circuit design to reduce the system power and improve the frequency as well. Further study reveals that the performance of the proposed design depends strongly on the choice of tuning voltage value, which should be paid much attention to obtain a proper trade-off between power and speed in application.

The most attractive merit of tunneling carbon nanotube field effect transistors (T-CNFETs) is the ultra-small inverse sub-threshold slope. In order to obtain as small an average sub-threshold slope as possible, several effective approaches have been proposed based on a numerical insight into the working mechanism of T-CNFETs: tuning the doping level of source/drain leads, minimizing the quantum capacitance value via tuning the bias condition or increasing the insulator capacitance, and adopting a staircase doping strategy in the drain lead. Non-equilibrium Green's function based simulation results show that all these approaches can contribute to a smaller average inverse sub-threshold slope, which is quite desirable in high-frequency or low-power applications.