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.