In Situ Selenized Back‐to‐Back WSe 2 /W/Ge Dual Schottky Heterojunction for Broadband High‐Speed Polarization‐Encoded Communication

ABSTRACT Mixed‐dimensional van der Waals heterostructures comprising 2D transition metal dichalcogenides (TMDs) and 3D semiconductors show great promise for short‐wave infrared (SWIR) photodetection. In this study, breaking through the limitations of traditional thin‐film transfer processes, the in situ fabrication of WSe 2 /W/Ge back‐to‐back dual Schottky heterojunctions on Ge substrates is successfully achieved via a W passivation barrier‐assisted in situ selenization technique, which effectively suppresses the formation of GeSe by‐products. An 8 × 8 photodetector array is fabricated, exhibiting significant photoresponse in the broad spectral range of 532–2200 nm. Specifically, the responsivity () and specific detectivity () at 1550 nm are as high as 2.77 A/W and 1.55 × 10 12 Jones, respectively. The device exhibits a unique double‐exponential decay characteristic, arising from synergistic fast and slow carrier transport in the back‐to‐back dual Schottky structure. The mechanism constitutes the physical origin of the high‐speed photoresponse in the device, achieving response speeds of 1.70/1.67 and 0.19/0.88 µs, along with 3 dB cutoff frequencies () of 198 and 385 kHz, respectively. The device enables high‐resolution SWIR polarization imaging and high‐speed communication, offering a novel architecture for next‐generation SWIR photodetectors.