Bias-independent subthreshold swing in ballistic cold-source field-effect transistors by drain density-of-states engineering

Low power consumption and stable performance insensitive to power supply are highly required for field-effect transistors integrated in portable technologies. Here, we report a mechanism of bias-independent sub-60 mV/dec subthreshold swing (SS) in ballistic cold-source field-effect transistors (CS-FETs) for portable electronics. Our first-principles and quantum-transport simulations demonstrate that, in the ballistic-transport regime, the energy alignment of the number of conduction modes (NOCM) between the drain and source electrodes is critical to achieving bias-independent SS of C-31/MoS2-based CS-FETs. By revealing the connection between NOCM and density of states (DOS), we propose a device model to demonstrate how similar slopes of the NOCM and DOS in the drain falling into the gate window can stabilize the SS of the devices under different bias. This study underscores the significance of drain DOS engineering in the design of bias-insensitive CS-FETs for portable electronic applications.