Ultrafast 27 GHz cutoff frequency in vertical WSe2 Schottky diodes with extremely low contact resistance.

Ultra-thin two-dimensional semiconducting crystals in their monolayer and few-layer forms show promising aspects in nanoelectronic applications. However, the ultra-thin nature of two-dimensional crystals inevitably results in high contact resistance from limited channel/contact volume as well as device-to-device variability, which seriously limit reliable applications using two-dimensional semiconductors. Here, we incorporate rather thick two-dimensional layered semiconducting crystals for reliable vertical diodes showing excellent Ohmic and Schottky contacts. Using the vertical transport of WSe2, we demonstrate devices which are functional at various frequency ranges from megahertz AM demodulation of audio signals, to gigahertz rectification for fifth-generation wireless electronics, to ultraviolet-visible photodetection. The WSe2 exhibits an excellent Ohmic contact to bottom platinum electrode with record-low contact resistance (~50 Ω) and an exemplary Schottky junction to top transparent conducting oxide electrode. Our semitransparent vertical WSe2 Schottky diodes could be a key component of future high frequency electronics in the era of fifth-generation wireless communication.