Waveguide-integrated 2D-material infrared photodetectors: fundamentals, advances, and insights

Photodetectors that integrate two-dimensional (2D) materials with optical waveguides are considered an ideal approach to enhance infrared detection capability and on-chip integration capability and have become a focal point of recent research. These devices benefit not only from the intrinsic optoelectronic properties and flexible hetero-integration of 2D materials but also from a range of engineering strategies that enable precise control over their electronic and optical characteristics. In addition, by combining different types of waveguide structures, the optical field distribution can be effectively tailored, further strengthening light-matter interactions and facilitating the realization of compact, high-performance infrared photodetectors with versatile strategies. This review systematically summarizes the latest progress in waveguide-integrated 2D-material infrared photodetectors, organized primarily by the type of waveguide material and further categorized according to the 2D materials employed. It discusses the advantages of various waveguide structures and 2D materials, the working mechanisms, performance parameters, common device architectures, and many key approaches to improving photodetector performance (e.g., waveguide structure optimization, electrode material and spacing design, gate electrostatic doping, substrate engineering, strain modulation, twist angle control of 2D materials, heterojunction band alignment, etc). Furthermore, a comparative analysis with conventional commercial photodetectors is provided, demonstrating that waveguide-integrated 2D-material infrared photodetectors have already achieved comparable performance in many applications, while certain challenges remain. Finally, the review outlines the key obstacles facing practical implementation and offers perspectives on future research directions.