Opitimization of tunneling based on stair-case carbon nanotube-FETs doping strategy

Due to the fact that either holes or electrons can band-to-band-tunnel （BTBT） through channelsource/drain contacts, tunneling carbon nanotube field effect transistors （T-CNFETs） suffer from ambipolar transporting characteristic. To suppress such ambipolar conductance, a novel device design based on stair-case doping strategy of drain region is proposed first in this paper. The dependences of available ON-OFF current ratio, practical ON-OFF current ratio with certain gate bias range and the average sub-threshold swing on the doping level of drain region are studied. Simulation results show that such device design can not only increase the ON-OFF current ratio largely but also result in a clear decrease of sub-threshold swing. At the same time, however, such stair-case doping strategy would broaden the depletion region and result in an increase of device area cost. Particular attention should be paid to the choice of doping level of drain region to make a proper tradeoff between power, speed and area in application.