Performance optimization of conventional MOS-like carbon nanotube FETs with realistic contacts based on stair-case doping strategy

Due to carriers’ band-to-band tunneling (BTBT) at channel–source/drain contacts, conventional MOS-like carbon nanotube field effect transistors (C-CNFETs) suffer from ambipolar transport property. To reduce such ambipolar conductance, a stair-case doping strategy in drain lead of C-CNFETs is proposed firstly in this paper. The non-equilibrium Green’s function (NEGF)-based simulation results show that, due to the elimination of BTBT at channel–drain contacts, such stair-case doping strategy improves the OFF-state performance greatly, although the band pinning at channel–drain contact has a slight impact on the ON-state performance of the device. Then, a comparison between the performance of such doping strategy and that of previous research work has been drawn, and the simulation results reveal that this doping strategy contributes to a much greater reduction in ambipolar conductance and increase in ON–OFF current ratio, which are quite desirable in low-power applications. Further research reveals that even higher device performance can be obtained with such stair-case doping strategy adopted in both source and drain leads than just in drain lead, but at the cost of larger device area. Therefore, much attention should be paid to the choice of device structure and doping concentration to make a proper tradeoff among power, speed and area in application. At last, C-CNFETs with all kinds of realistic contacting situations are studied, and the results show that this stair-case doping strategy can improve the performance of C-CNFETs greatly even with Schottky contact taken into account.