Response Speed-Tunable Photodetectors Based on Hybrid Ternary FePSe₃ Nanoflakes

The layered metal phosphorus trichalcogenides (MPTs) are a newly emerging van der Waals material family with bandgaps ranging from 1.3 to 3.5 eV, which are promising candidates for optoelectronic devices. By using the excited multiple energy levels of FePSe₃, a high-performance FePSe₃ photodetector, which shows tunable response speed in the range of ultraviolet (UV) to near-infrared (NIR), is designed. The FePSe₃ photodetector exhibits a high photoresponsivity of 236.18 A·W⁻¹ under 532 nm laser illumination (laser power density P = 1 mW cm⁻²). The properties of FePSe₃ can be modulated by oxygen plasma treatment, which transfer to oxygen-doped FePSe₃ (FePSe₃-O). Moreover, the speed of the FePSe₃-O photodetector can be improved more than 240 times compared to the intrinsic FePSe₃ photodetector under NIR illumination (λ = 808 nm). In addition, the FePSe₃-graphene heterojunction can significantly improve the photoresponsivity and simultaneously prolong the response time of the device due to the FePSe₃/graphene interfacial barrier. These results suggest that intrinsic, doped FePSe₃ and its heterojunction can be used as multifunctional photodetectors with tunable response speeds.