Above 300 GHz Ultrafast Cutoff Frequency Achieved via Air Gap‐Induced Capacitance in van der Waals ReSe ₂ Schottky Diodes

ABSTRACT Sub‐terahertz ultrahigh cutoff frequencies (f C ) are achieved from a van der Waals material rhenium diselenide (ReSe 2 )‐based vertical Schottky diode, when the diode architecture is specially designed with an air gap between 100 nm‐thick ReSe 2 and Ohmic contact electrode. The maximum intrinsic f C of our diode reaches 430 GHz, the highest among the reported thin film‐based RF diodes. With the increase of air gap size, the intrinsic f C of each diode rises from ∼30 GHz (without an air gap) to 310–430 GHz. The extrinsic f C , measured from RF rectifier circuits using the air gap‐containing Schottky diode, also increases from 2 to 40 GHz. The underlying principle behind these f C enhancements is investigated using an equivalent circuit model, which closely matches the experimental results. Our air gap engineering provides a practical strategy to improve the f C of vertical Schottky diodes, opening new avenues for 2D material‐based RF electronics.