Analysis of Source Doping Effect in Tunnel FETs With Staggered Bandgap

The effect of source doping on tunnel FET (TFET) currents is investigated analytically for the case of an exponential barrier. Source depletion is coupled to the channel potential profile through the continuity of field at the junction edge. Closed form WKB (Wentzel-Kramers-Brillouin) integral are carried out by considering mixed electron and hole tunneling in heterojunction TFETs with a staggered bandgap. It is shown that there is an optimum source doping that maximizes the TFET current. A certain degree of source depletion actually helps because it lets low-barrier hole tunneling in the source to make up part of the tunneling path.