Thermionic emission-dominated sub-60 mV/dec operation in BSb/CNT van der Waals heterostructure transistors

The continuous scaling of metal-oxide-semiconductor field-effect transistors (MOSFETs) is fundamentally limited by short-channel effects and the Boltzmann tyranny, which imposes a minimum subthreshold swing (SS) of 60 mV/dec at room temperature. In this work, we propose a steep-slope cold-source FET (CS-FET) leveraging a van der Waals heterostructure of monolayer BSb and an (8,0) carbon nanotube (CNT). Through first-principles quantum transport simulations, we demonstrate that the BSb/CNT CS-FET achieves record-low SS values of 28.9-56.8 mV/dec at ultra-low supply voltages of 0.2-0.4 V, outperforming graphene/CNT CS-FETs (72.1 mV/dec) and CNT tunnel FETs (108.2 mV/dec). Analysis of the current distribution reveals that thermionic emission dominates carrier injection, contributing over 99.2%. The super-exponential decay of electron concentration in BSb effectively suppress the Boltzmann thermal tail, enabling sub-60 mV/dec switching behavior. These findings highlight the potential of BSb/CNT heterostructures for next-generation ultra-low-power electronics, offering a promising pathway to overcome the limitations of conventional MOSFETs.