Quantum mechanical performance predictions of p-n-i-n versus pocketed line tunnel field-effect transistors

The tunnel field-effect transistor (TFET) is a promising candidate to replace the metal-oxide-semiconductor field-effect transistor in advanced technology nodes, because of its potential to obtain sub-60 mV/dec subthreshold swings. However, it is challenging to reach sufficiently high on-currents in TFETs. Therefore, on-current boosters are actively being researched. In this paper, a p-n-i-n TFET, containing a vertical pocket at the source-channel junction, is studied with quantum mechanical simulations and compared with a line tunneling TFET, containing horizontal pockets in the source region. The comparison is carried out both for all-Si and all-Ge, while an extrapolation is made for smaller bandgap materials. The p-n-i-n TFET is found to perform better than a p-i-n configuration, thanks to the increased electric field at the source-pocket junction. Compared to the p-n-i-n TFET, the line TFET has an even higher on-current and lower subthreshold swing, attributed to the closer proximity of the tunnel junction to the gate. For the all-Ge case, the difference between the two configurations is found to decrease when direct transitions are taken into account semi-classically.