High-Performance\nVisible-to-SWIR Photodetector Based\non the Layered WS<sub>2</sub> Heterojunction with Light-Trapping Pyramidal\nBlack Germanium

This study presents a layered transition\nmetal dichalcogenide/black\ngermanium (b-Ge) heterojunction photodetector that exhibits superior\nperformance across a broad spectrum of wavelengths spanning from visible\n(vis) to shortwave infrared (SWIR). The photodetector includes a thin\nlayer of b-Ge, which is created by wet etching of germanium (Ge) wafer\nto form submicrometer pyramidal structures. On top of this b-Ge layer,\nthe WS<sub>2</sub> thin film is deposited using pulsed laser deposition.\nIn comparison to conventional germanium, b-Ge absorbs about 25% more\nlight between 850 and 1750 nm wavelengths. The WS<sub>2</sub>/b-Ge\nphotodetector has a peak photoresponsivity of 0.65 A/W, which is more\nthan twice the photoresponsivity of the WS<sub>2</sub>/Ge photodetector\nat 1540 nm. Additionally, it shows better responsivity and response\nspeed compared with other similar state-of-the-art photodetectors.\nSuch an improvement in the performance of the device is credited to\nthe light-trapping effect enabled by the germanium pyramids. Theoretical\nsimulations employing the finite-difference time-domain technique\nhelp validate the concept. This novel photodetector holds promise\nfor efficient detection of light across the vis to SWIR spectrum.