Doping, Tunnel Barriers, and Cold Carriers in InAs and InSb Nanowire Tunnel Transistors

InAs and InSb nanowire tunnel field-effect transistors require highly degenerate source doping to support the high electric fields in the tunnel region. For a target on-current of 1 μA, the source Fermi energy lies in the range of 0.1-0.22 eV below the valence band edge depending on the material and diameter. Despite the large degeneracy, the devices achieve minimum inverse subthreshold slopes of ~ 30 mV/dec. In the subthreshold, these devices experience both regimes of “voltage-controlled tunneling” and “cold-carrier injection.” The reduction of the inverse subthreshold slope from each of these two processes is quantified. Numerical results based on a discretized eight-band k-p model are compared to analytical WKB theory. The standard WKB theory gives good qualitative agreement with the full-band numerical simulations.