Tunable electronic structures in Type-II PtSe2/HfS2 van der Waals heterostructure by external electric field and strain

Based on first-principles calculations, we investigate in detail the structural stability and electron-optical properties of monolayer PtSe2, HfS2, and two-dimensional (2D) PtSe2/HfS2 van der Waals (vdW) heterostructure. The results show that 0.57eV indirect bandgap semiconductor and Type-II band alignment are formed at the PtSe2/HfS2 vdW heterostructure, which greatly promotes the effective separation of photogenerated electrons and holes. It is worth mentioning that the heterostructure exhibits a wider light absorption range and a higher light absorption intensity. The band structure of the heterostructure can be changed significantly by applying an applied electric field, but the Type-II band alignment remains all the time, and the transition from semiconductor to metal occurs when the critical electric field is reached. In addition, the PtSe2/HfS2 heterostructure changes from Type-II to Type-I band alignment under different biaxial strains, while the heterostructure keeps the Type-II band alignment under uniaxial strains, and changes from semiconductor to metal with the increase of strain. It is worth noting that the heterostructure is sensitive to compressive strain but insensitive to tensile strain, which provides theoretical guidance for photoelectric devices in specific environments. These results indicate that PtSe2/HfS2 heterostructure will be widely used in photodetectors and nanodevices.