The current status and challenges of two-dimensional infrared detectors based on interlayer excitons

Transition metal dichalcogenides (TMDs) van der Waals heterojunctions, characterized by atomically flat interfaces and the absence of surface dangling bonds, have emerged as a revolutionary platform for novel optoelectronic devices by overcoming the lattice-mismatch limitations inherent in traditional heterostructures. Through the synergistic effect of band engineering and interlayer exciton modulation, van der Waals heterojunctions effectively overcome these challenges in traditional infrared detectors, such as high dark current, slow response speed, and poor environmental stability. The core mechanism in the formation of a unique type-II band alignment by designing the stacking mode of the heterointerface, which induces charge transfer at the heterojunction interface and generates interlayer excitons with long carrier lifetimes (up to the microsecond level). Compared to monolayer TMDs with restricted exciton transport properties, interlayer excitons exhibit unique advantages such as tunable energy band, extended lifetime, and broad spectral response, positioning them as a focal point in two-dimensional (2D) infrared detector research. This review systematically elaborates on the main mechanisms of photodetectors, including photoconductive, photovoltaic, and photothermal effects. Notably, photovoltaic-based 2D infrared detectors exhibit superior performance, such as high responsivity, rapid response speed, and broadband detection capability. It can effectively suppress dark current and improve the signal-to-noise ratio. Subsequent sections discuss the photodetection mechanism and advantages of interlayer excitons in 2D infrared detectors. We further review the preparation process of 2D interlayer exciton infrared detectors, including heterojunction preparation methods such as mechanical exfoliation, device architecture design such as optical waveguide structures, and electrode preparation and packaging technologies. Methods such as mechanical exfoliation, chemical vapor deposition, and molecular beam epitaxy are used to construct high-quality heterojunctions. Device structure design focuses on vertical stacking of built-in electric fields, optical waveguide integration, and ultra-short channel structures to shorten the carrier transport path and enhance light absorption. Packaging technology improves environmental stability through protective layers such as Al2O3 and h-BN. However, the large-scale preparation of van der Waals heterojunctions remains a challenge, which brings difficulties to commercialization and is full of opportunities and challenges. Finally, we highlight the key progress in research and applications of interlayer exciton infrared detectors. These include self-powered detectors, polarization-sensitive detectors, and superlattice infrared detectors. The self-powered infrared detector utilizes the built-in electric field of type-II heterojunctions to achieve zero-bias operation with low dark current. The polarization detector achieves spectral selectivity response through anisotropic materials and realizes a large polarization ratio. The superlattice detector combined with band engineering has achieved an extremely high absorption in the long-wave band, breaking through the performance limits of traditional detectors. Finally, the development prospects of 2D infrared detectors based on interlayer excitons are discussed. These devices have broad prospects in applications such as all-optical modulators, imaging systems, image sensors, and flexible photodetectors.