Reduction of TFET OFF-Current and Subthreshold Swing by Lightly Doped Drain

This brief models the effect of lightly doped drain on the $I_{\mathrm { {ds}}}$ – $V_{\mathrm { {gs}}}$ and $I_{\mathrm { {ds}}}$ – $V_{\mathrm { {ds}}}$ characteristics of tunnel FETs. It is shown that an extended drain depletion region can greatly reduce both the off-current and the subthreshold swing with essentially no impact on the on-current. In particular, a lightly doped drain mitigates the undesirable ambipolar effect that cannot otherwise be relieved by lengthening the channel length. However, if the density of states is not sufficiently low, a low drain doping could result in a nondegenerate condition in which the tunneling window is blocked at $V_{\mathrm { {ds}}} = 0$ , degrading the linear region current.