Cross‐Substitution Promoted Ultrawide Bandgap up to 4.5 eV in a 2D Semiconductor: Gallium Thiophosphate

-based photodetector exhibits polarization-sensitive photoresponse with a linear dichroic ratio of 1.85 at 254 nm, benefitting from its in-plane structural anisotropy. These results provide a pathway for the discovery and fabrication of 2D UWBS anisotropic materials, which become promising candidates for future solar-blind ultraviolet and polarization-sensitive sensors.