Numerical analysis of band tails in nanowires and their effects on the performance of tunneling field-effect transistors

Band tails in heavily doped semiconductors are one of the important parameters that determine transfer characteristics of tunneling field-effect transistors. In this study, doping concentration and doing profile dependences of band tails in heavily doped Si nanowires were analyzed by a nonequilibrium Green function method. From the calculated band tails, transfer characteristics of nanowire tunnel field-effect transistors were numerically analyzed by Wentzel-Kramer-Brillouin approximation with exponential barriers. The calculated transfer characteristics demonstrate that the band tails induced by dopants degrade the subthreshold slopes of Si nanowires from 5 to 56mV/dec in the worst case. On the other hand, surface doping leads to a high drain current while maintaining a small subthreshold slope.