An Ultrahigh-Contrast Violet Phosphorus Van der Waals Phototransistor

Ultrahigh-contrast photodetection with low background noise is of critical importance for accurate image-sensing in deep-sea and deep-space exploration. The state-of-the-art silicon and III–V semiconductor-based photodetectors usually require extended exposure to incident light for high-quality sensing in darkness, which unfortunately results in large room temperature dark currents (RT-I_dark) and deteriorates the expected imaging contrasts. Herein, a high-performance violet phosphorus (VP) phototransistor is reported by constructing a trap-free interface between the VP channel and hexagonal boron nitride (h-BN) dielectric via perfect van der Waals stacking. The device shows an extremely low RT-I_dark of 80 fA and gate-tunable high ON/OFF ratio over 10⁵, which is 2–4 orders of magnitude superior to that of conventional counterparts. A VP photodetector array has been fabricated to demonstrate the high-contrast image-sensing capability. The findings demonstrate the effectiveness of VP in low background noise and ultrahigh-contrast image-sensing applications, while also presenting exciting opportunities to enhance interface qualities through van der Waals architectures for high-performance optoelectronics.