Type II Homo-Type Bi₂O₂Se Nanosheet/InSe Nanoflake Heterostructures for Self-Driven Broadband Visible–Near-Infrared Photodetectors

Abstract

Bi₂O₂Se nanosheets, an emerging ternary non-van der Waals two-dimensional (2D) material, have garnered considerable research attention in recent years owing to their robust air stability, narrow indirect bandgap, high mobility, and diverse intriguing properties. However, most of them show high dark current and relatively low light on/off ratio and slow response speed because of the large charge carrier concentration and bolometric effect, hindering their further application in low-energy-consuming optoelectronics. Herein, a homotype van der Waals heterostructure based on exfoliated n-InSe integrated with chemical vapor deposition (CVD)-grown n-Bi₂O₂Se nanosheets that have type II band alignment was fabricated. The efficient interfacial charge separation, strong interlayer coupling, and effective built-in electric field across the heterointerface demonstrated excellent, stable, and broadband self-driven photodetection in the range 400-1064 nm. Specifically, a high responsivity (R) of 75.2 mA·W^-1 and a high specific detectivity (D*) of 1.08 × 10¹² jones were achieved under 405 nm illumination. Additionally, a high R of 13.3 mA·W^-1 and a high D* of 2.06 × 10¹¹ jones were achieved under 980 nm illumination. Meanwhile, an ultrahigh I_light/I_dark ratio over 10⁵ and a fast response time of 5.8/15 ms under 405 nm illumination confirmed the excellent photosensitivity and fast response behavior. Furthermore, R could be enhanced to 13.6 and 791 mA·W^-1 under 405 and 980 nm illumination at a drain-source voltage (V_ds) of 1 V, respectively, originating from a lower potential barrier. This study suggested that the Bi₂O₂Se nanosheet/InSe nanoflake homotype heterojunction can offer potential applications in next-generation broadband photodetectors that consume low energy and exhibit high performance.