High responsivity p-GaSe/n-Si van der Waals heterojunction phototransistor with a Schottky barrier collector for ultraviolet to near-infrared band detection

Broadband high-performance photodetector operating at ultraviolet (UV) to infrared (IR) wavelengths is critical for numerous applications ranging from environmental sensing, medical diagnostics, to high-resolution spectroscopy. In this Letter, a p-GaSe/n-Si van der Waals heterojunction phototransistor (HPT) with a Schottky barrier (SB) collector on silicon-on-insulator is proposed and demonstrated to secure sensitive detection at UV (270 nm) to near-IR (1500 nm) wavelengths. Remarkable responsivities of 114 A/W at 275 nm and 1.3 A/W at 1550 nm as well as large specific detectivities of >1011 Jones at 275 nm and 1.1 × 109 Jones at 1500 nm are achieved. The absorption of UV and visible light mainly occurs in GaSe emitter and Si base. While the construction of Pt/n-Si SB enables extended IR response (>1107 nm) by the internal photoemission effect (IPE) and effectively suppresses the dark current of the HPT to a low value of 0.5 nA at a bias of 5 V simultaneously. The huge hole/electron injection ratio resulted from the large energy bandgap offset between GaSe and Si significantly amplifies the photocurrent. In combination with the resonant cavity modulation effect, a high photocurrent gain is produced in the HPT. These results demonstrate that the two-terminal mixed-dimensional p-GaSe/n-Si HPT with a SB collector is a promising candidate for extending the response wavelength to both UV and NIR bands.