Broadband and Ultra-High-Sensitivity Separate Absorption–Multiplication Avalanche Phototransistor Based on a Au–WSe2–Ge Heterostructure

Avalanche photodetectors (APDs) with ultrahigh sensitivity across a wide spectral range are highly desirable for optical communication, laser radar imaging, biomedical detection, and atmospheric and astronomical observation applications. Here, we present a separate absorption and multiplication (SAM) APD based on a Au/WSe2/Ge heterostructure, where the infrared absorption and avalanche regions are in the Ge substrate and the Au/WSe2 Schottky junction, respectively. Compared with the dark current of a WSe2/Ge photodetector (1 × 10–9 A), the SAM-type heterostructure exhibits significantly reduced dark current as low as 2 × 10–11 A and a remarkable avalanche multiplication effect. The inherent mechanism is studied based on the positive temperature coefficient of the breakdown voltage, photocurrent mapping experiments, Sentaurus TCAD simulation, and energy band analysis. Especially, this device achieves extremely high avalanche gains in the infrared range, reaching 1297 and 4100 at 1310 and 1550 nm, respectively. At the same time, in the visible light band, the device still achieves a high avalanche gain of 500 under 532 nm illumination with rise/fall times of 8/8.2 μs, respectively, demonstrating the excellent broadband avalanche photodetection capability of the device. These results demonstrate that the SAM-type heterostructure APD is promising for low-dark-current, wide-band, and high-gain avalanche photodetection applied in laser radar imaging and single-photon detection systems.