Bias-Selectable Dual-Band Avalanche Detector Based on Au-WS₂-Ge Heterostructure

Here, we report a bias-selectable visible and near-infrared photoresponses due to stacked back-to-back diodes structure in a mixed-dimensional Au-WS2-Ge avalanche photodetector. Controllable switching between Schottky (Au/WS2) and PN (WS2/Ge) junctions can be realized depending on the polarity of the bias voltage. Therefore, this device can provide bias-dependent single-band (visible) and fused-band (visible&near-infrared) avalanche detection modes. When the Schottky junction is reversed, ultra-high responsivity (over 2000 A/W) and gain (349) at 532 nm can be obtained when reaching the avalanche breakdown (single-band mode). Meanwhile, when the PN junction is reversed, the ultra-high gains around 354 and 519 can be realized at both 532 and 1550 nm, respectively (fused-band mode). The simulated I-V features agree well with the experimental results. This device provides a novel direction for the application of integrated dual-band avalanche devices in optoelectronic detection.