Self-Powered Bipolar Response Photodetector Based on MoS2/SnBi2Te4 Heterojunction.

Self-powered detectors with bipolar photoresponse have significant potential applications across various fields. However, achieving both fast response and high-sensitivity simultaneously in a single bipolar photodetector remains a challenge. In this study, we present a self-powered photodetector based on a MoS2/SnBi2Te4 unipolar barrier van der Waals heterojunction, which exhibits a wavelength-dependent bipolar photoresponse. This unique behavior arises from the switching dominance of the two materials in the device photoresponse at different wavelengths. The device demonstrates a negative photoresponse in the wavelength range of 532-808 nm, achieving a noise equivalent power (NEP) as low as 3.35 × 10-15 W·Hz-1/2 at 635 nm, along with an impressive specific detectivity (D*) of 1.26 × 1011 Jones. Notably, it exhibits a positive photoresponse among the wavelengths of 980-1250 nm, with an NEP value of 3.06 × 10-14 W·Hz-1/2 and a D* of 1.38 × 1010 Jones at 980 nm. Furthermore, we demonstrate the potential application of this detector in ternary optical logic devices. Additionally, the unipolar barrier band structure effectively suppresses carrier recombination, while the built-in electric field facilitates rapid charge separation. As a result, the device achieves an ultralow dark current and fast response speeds, with a rise time of 2.3 μs and a fall time of 4.2 μs. This study offers innovative material architectures and design strategies for constructing self-powered bipolar photodetectors with high sensitivity.