Device Physics of Germanium-Junctionless Tunnel Field Effect Transistor and an Approach to Optimize I _on/I _off by Drain Engineering and Work Function Engineering

We demonstrate the physics behind the operation of Germanium (Ge) junctionless tunnel field effect transistor (JLTFET) for high performance and low power (LP) logic applications. Due to increasing rate of band to band tunneling (BTBT) for low band gap semiconductors like germanium, the subthreshold leakage in the OFF state increases rapidly when compared with the increase in ON state current. The tunneling rate on the drain side can be effectively suppressed by engineering the drain doping variation and conscientious work function engineering. By making the concentration of drain side lower, we can have a wider tunneling width (w _T) and a compressed electric field (E) in the drain side, which henceforth reduces the I _off considerably. Appropriate selection of work function for source and drain side gate metal of a double metal gate (DMG) Ge-JLTFET can also significantly reduce the OFF state leakage and hence gives ameliorated I _on/I _off. The results show that both drain engineering and work function engineering techniques can be applied to low band gap tunneling transistors for superior electrostatic integrity and better scalability.