Broadband Avalanche Photodetector With Low Breakdown Voltage Based on WSe 2 /Ge Heterojunction-Assisted

Avalanche photodetectors (APDs) leverage internal avalanche multiplication effects to significantly boost photoelectric conversion gain, making them ideal devices for high-sensitivity detection of weak optical signals. In this work, we demonstrate the Au/WSe2/Ge Schottky-heterojunction (S-HJ) APD that enables low-voltage avalanche breakdown via heterojunction-assisted carrier acceleration. Under reverse bias, the device exhibits an extremely low dark current (on the pA scale), with an avalanche breakdown voltage as low as approximately 31 V—nearly 50% lower than that of WSe2/Au Schottky-type APDs (approximately 62 V) in the same material system. When irradiated at 532 and 1550 nm, the device achieves a high responsivity of 556 and 20 A/W, respectively. Mechanistic analysis reveals that under reverse bias, the built-in electric field of the WSe2/Ge heterojunction accelerates and efficiently extracts the avalanche-multiplied carriers from the Au/WSe2Schottky junction, thereby facilitating impact ionization and significantly reducing the external bias required for avalanche breakdown. This work proposes a novel heterojunction-assisted avalanche mechanism, providing a feasible pathway toward next-generation APDs featuring low operating voltage, high gain, and broadband spectral response.