Polarization‐Sensitive Momentum‐Matching Interlayer Excitons for Infrared Photodetection

2D materials hold potential for developing low‐cost, high‐performance broadband polarized infrared photodetectors. However, the development of 2D broadband polarized infrared photodetectors is largely constrained by the fixed bandgap spectral (cutoff wavelength) limitations of available semiconductors. Here, an approach is presented that leverages anisotropic interlayer excitons (IEXs) within a type‐II van der Waals heterojunction, achieving polarization photoresponse beyond the intrinsic bandgap spectral limits of its constituent semiconductors. By constructing heterojunctions using CrPS4 and ReS2, a unique type‐II band alignment, enabling strong anisotropic optical excitation is achieved through the interlayer sub‐bandgap, which is lower than the intrinsic bandgaps of both CrPS4 and ReS2. The heterojunction exhibits a responsivity of 0.3 A W−1 and a polarization ratio of 1.3 at an incident photon energy of 0.8 eV, comparable to naturally anisotropic materials with intrinsic bandgaps. Additionally, the potential of anisotropic IEXs is demonstrated for dual‐band polarization detection by introducing a ReS2/CrPS4/MoS2 heterojunctions with distinct inte rlayer sub‐bandgaps. This flexible design of IEXs offers a new platform for multi‐dimensional optical sensing and on‐chip optoelectronic applications.