Doping-Free Cold-Source Contacts for BSb/InSe van der Waals Transistors with Sub-60 mV/Decade Subthreshold Swing

The relentless scaling of transistors has intensified power dissipation challenges in modern integrated circuits, necessitating devices that operate below the fundamental Boltzmann limit of 60 mV/dec subthreshold swing (SS). Here, we propose a cold-source field-effect transistor (CS-FET) based on a van der Waals (vdW) heterostructure, comprising theoretically proposed monolayer boron antimonide (BSb) as the source electrode and indium selenide (InSe) as the channel. Through first-principles density functional theory (DFT) and quantum transport simulations, we demonstrate that the BSb/InSe FET intrinsically enables cold-source operation without intentional source doping. Specifically, the unique electronic band structure of the BSb electrode acts as a natural energy filter, truncating the high-energy tail of the Fermi-Dirac distribution and effectively suppressing the injection of thermally excited hot electrons into the channel. Driven by this carrier-cooling mechanism, the device achieves an ultralow SS of 38.14 mV/dec at room temperature, outperforming conventional metal-oxide-semiconductor field-effect transistors (MOSFETs) and state-of-the-art graphene-based CS-FETs (68.74 mV/dec). Furthermore, it delivers outstanding on-state currents of 1295.33 nA/nm for high-performance and 907.42 nA/nm for low-power applications, fully satisfying the International Roadmap for Devices and Systems (IRDS) 2028 targets. This work establishes BSb as a compelling, doping-free alternative to graphene for next-generation cold-source electrodes, providing a theoretical framework for ultralow-power 2D logic electronics.