Axial Si/Ge hetero-nanowires for tunneling transistors

Modern vapor-liquid-solid (VLS) growth based on alloy catalysts can grow SiGe heteronanowires (hetero-NWs) with controlled axial heterojunction abruptness [1] combined with simultaneous control of material composition (Si and Ge) and doping profile. Previously, we reported on axial in-situ doped Ge NW pn junction tunneling field effect transistors (TFETs) with effective backgate control of the tunneling current [2]. In this presentation, we report on tri-gated p-Ge/i-Si/n-Si axial hetero-NWs TFET with on-state tunneling occuring in the Ge drain section and off-state leakage dominated by the Si junction in the source. The devices have high Ion of 2 uA/um, suppressed ambipolarity, and a sub-threshold slope SS of 140 mV/decade over 4 decades of current with lowest SS of 50 mV/decade. Device operation in the tunneling mode is confirmed by three-dimensional TCAD simulation. In addition, our devices work standard as NW FETs with good Ion/Ioff ratio when the source-drain junction is forward-biased [3]. [1] D. E. Perea et al., Nano Lett 11, 3117 (2011). [2] Son T. Le et al., Appl. Phys. Lett. 96, 262102 (2010). [3] Son T. Le et al., accepted to Nano Lett. (10/2012).