Towards direct band-to-band tunneling in P-channel tunneling field effect transistor (TFET): Technology enablement by Germanium-tin (GeSn)

Tunneling field-effect transistor (TFET) could achieve sub-60 mV/decade subthreshold swing S at room temperature and could enable ultra-low supply voltage V_DD and power consumption. Drive current above 100 μA/μm was achieved in III-V-based n-channel TFETs (nTFETs), due to the direct BTBT and high electron mobility in III-V materials [1-2]. However, more research is needed for p-channel TFET (pTFET). While III-V materials have high direct band-to-band tunneling (BTBT) rate, hole mobilities are generally low and lead to high channel resistance [Fig. 1(b)]. SiGe or Ge have high hole mobility and might be promising for pTFETs, but the the BTBT is indirect and the on-state current is low. Also, high activation temperature and large diffusivity of n-type dopants in Ge make it very difficult to form good N⁺/P junction in Ge.