Vertically Stacked Short Channel PtSe₂/Ultrathin‐Silicon Heterojunction for Fast‐Speed UV Photodetection Application

Abstract Superior ultraviolet photodetectors (UVPDs) with fast response speed and high responsivity are essential for UV communication, intelligent sensing, advanced manufacturing, and more. Various studies have demonstrated the excellent performance of traditional UVPDs based on wide bandgap semiconductors (WBSs). However, these devices often suffer from a relatively slow response speed due to the defect states within WBSs. In this work, a new short channel non‐WBS UVPD is developed using the vertically stacked short channel PtSe₂/ultrathin‐Si UVPD. The heterojunction is stacked by the 200 nm thick Si flake that exfoliates from a Silicon‐on‐Insulator (SOI) wafer by wet etching and the wafer‐scale CVD ‐grown PtSe₂ via the mature PDMS stamp transfer protocols. The absorption in the Si layer, which depends on the incident wavelength, shows a strong correlation with the device photocurrent response. Under 365 nm illumination, the vertical device exhibits a fast UV response speed up to 51.8/73.6 µs. This performance outperforms that of conventional lateral structures and many WBS‐based UVPDs, largely attributed to the extremely short transport distances of photogenerated carriers and the superior physical characteristics of Si. This study shows that ultrathin‐Si is a promising building block for fast speed UVPDs, which are vital for UV optoelectronic applications.