Using dimensionality to achieve a sharp tunneling FET (TFET) turn-on

In order to achieve significantly reduced power consumption, the transistor operating voltage needs to be reduced. To do this, a tunneling based transistor needs to rely on the density of states turn-on as shown in Fig 1 [1]. Current can only flow when the conduction and valence bands overlap. If the band edges are ideal, one might expect an infinitely sharp turn on when the band edges overlap. Surprisingly, in a typical 3d bulk TFET, the nature of the turn on is actually quadratic in the gate voltage. Nevertheless, it is possible improve this if dimensionality is reduced. Consequently, we explored the nature of the band overlap for the various dimensionalities shown in Fig 2. We find that a 2d-2d pn junction, as shown in Fig. 2(i) brings us significantly closer to an ideal step function. Confining each side of the pn junction will also significantly increase the on state conductivity at low voltages.