2. Heterojunction gate-drain underlap tunnel FET

A 2-D structure of the proposed UL-HTFET is shown in Figure 1. Here, a p + source and n + drain with an intrinsic channel and a δp + Si1-xGex layer at the source-channel tunnel junction are present. The δp + layer can be replaced by a δn + layer too.

Figure 1. A 2-D geometry of the device (UL-HTFET).

The effect of germanium mole fraction on the UL-HTFET is investigated. Aluminum with work function (4.1 eV) is considered as the gate material. The proposed device spans across a total length of 100 nm with a length of the channel equal to 20 nm. The δp + Si1-xGex layer extends from the source-channel junction up to 1 nm into the channel under the gate. The various doping concentrations are used such as source, 1021 cm<sup>3</sup> ; drain, 5 1019 cm<sup>3</sup> ; δp + layer, 1018 cm<sup>3</sup> ; and intrinsic region, 1016 cm<sup>3</sup> . In n-channel, the operation of TFET positive gate and drain voltages is applied with respect to the source. Here, voltage at the source is considered as the reference voltage.

The tunnel FET works on the principle of band-to-band tunneling. Here, SiGe layer is added at the channel near the source-channel junction to enhance the on-current.
