Type-II GeS/Ta ₂ NiSe ₅ Heterojunction Photodetector with Effectively Suppressed Dark Current

The emergent two-dimensional (2D) narrow bandgap (Eg) semiconductors are able to absorb at all visible wavelengths, possessing unique photoelectric properties with great potential in the field of photodetection and optical imaging. However, materials with narrow Eg usually suffer from a large internal dark current, which deteriorates their photoelectric performance. The built-in electric field (Eb) in the heterostructure can be effectively utilized to suppress the dark current of the device. Herein, we report the study of a type-II heterojunction device designed by vertically stacking low-dark-current GeS and high-photosensitivity Ta2NiSe5 flakes. The GeS/Ta2NiSe5 heterojunction is found to exhibit largely suppressed ultralow dark current of down to 10 pA compared to that of the single Ta2NiSe5 device and significantly enhanced photocurrent and photoresponse speed compared to that of the single GeS devices. Particularly, under illumination with a 405 nm laser, the device demonstrates a responsivity of up to 92.16 A/W, a detectivity of 2.23 × 1011 Jones, and a photocurrent on/off ratio around 103. Besides, the device can operate effectively in self-powered mode as well, with a responsivity of 11 mA/W. Indeed, the GeS/Ta2NiSe5 heterojunction demonstrates optical imaging with clear contrast in the visible range, showing excellent fatigue reliability and humid resistivity, highlighting its potential for future high-sensitivity, high-stability photodetecting systems. This work emphasizes band engineering as a strategy for optimizing the photoelectronic properties of 2D heterostructures while maintaining the advantages of single material, serving as a reliable reference for the design and development of future high-performance photoelectronics.