On the other hand, the increase of the gate voltage results in strong band to band tunneling near the drain contact. As a result the total current increases in the off-regime (Fig. 5.18-a) which has a detrimental effect on the device performance. Fig. 5.19-a shows that the parasitic current increases if the drain voltage becomes much higher than the gate voltage. For the device with symmetric doping we assumed that the donor and acceptor concentrations at the source and drain contacts are . By decreasing the doping of the drain side, the band bending decreases for the same gate voltage (Fig. 5.17-b) and the band to band tunneling current near the drain contact decreases considerably (see Fig. 5.18-b and Fig. 5.19-b). For the device with asymmetric doping profile, and .
M. Pourfath: Numerical Study of Quantum Transport in Carbon Nanotube-Based Transistors