Electronic and optical properties of a Ta2NiSe5 monolayer: A first-principles study

The crystal structure, stability, electronic, and optical properties of the Ta2NiSe5 monolayer have been investigated using first-principles calculations in combination with the Bethe–Salpeter equation. The results show that it is feasible to directly exfoliate a Ta2NiSe5 monolayer from the low-temperature monoclinic phase. The monolayer is stable and behaves as a normal narrow-gap semiconductor with neither spontaneous excitons nor non-trivial topology. Despite the quasi-particle and optical gaps of only 266 and 200 meV, respectively, its optically active exciton has a binding energy up to 66 meV and can exist at room temperature. This makes it valuable for applications in infrared photodetection, especially its inherent in-plane anisotropy adds to its value in polarization sensing. It is also found that the inclusion of spin–orbit coupling is theoretically necessary to properly elucidate the optical and excitonic properties of a monolayer.