We present a study about of the essential physical elements governing the OFF-state current in MOSFETs and tunnel FETs at truly nanoscale dimensions. By combining semianalytical models and full-quantum self-consistent simulations, we discuss the physical mechanisms responsible of the minimum OFF-current and of the ambipolarity of the current transfer characteristics. Moreover, we revisit the applicability of the natural transistor length as a metric for the shortchannel effects and assess the tunnel FETs potential to provide subthreshold swings below 60 mV/decade and better than their MOSFET counterparts for gate lengths approaching 10 nm.
