A Continuous Semianalytic Current Model for DG and NW TFETs

A continuous semianalytic $I$ – $V$ model is developed for double-gate (DG) and nanowire tunnel FETs (TFETs). At the core of the model is a gate-controlled channel potential that satisfies the source and drain boundary conditions. The band-to-band tunneling current is expressed in terms of Franz’s two-band $E(k)$ relation with 3-D density of states. Verified by numerical simulations, the model is capable of generating $I_{\mathrm{ ds}}$ – $V_{\mathrm{ gs}}$ characteristics for any a given bandgap and channel length, based on which the guidelines for TFET scaling are derived. A methodology for evaluating different $I_{\mathrm{\scriptscriptstyle ON}}$ – $I_{\mathrm{\scriptscriptstyle OFF}}$ characteristics, distinguished from the common practice of $I_{\mathrm{\scriptscriptstyle ON}}/I_{\mathrm{\scriptscriptstyle OFF}}$ ratio and SS slope, is employed. Ambipolar effect or channel-to-drain tunneling is also covered by the model. The model has been applied to an example of GaSb–InAs DG TFET, to compare with published atomistic simulation results. $I_{\mathrm{ ds}}$ – $V_{\mathrm{ ds}}$ characteristics are also generated by building into the model the debiasing effect of channel charge in the linear region.