Band Structures Transformation in Two-Faced Janus Monolayer SnXY(X, Y = O, S, Se, and Te)

In recent years, Janus single-layer materials have attracted researchers' interest due to their unique structures and potential applications. Inspired by the successful synthesis of Janus single-layer MoSSe, here we studied the electronic characteristics of Janus single-layer SnXY (X, Y = O, S, Se, and Te) through first-principles calculations. It is found that their parent configurations, SnX2 (X = O, S, Se and Te), have only two characteristics of indirect bandgap semiconductors and metals. However, the corresponding Janus single-layer structures are not only indirect bandgap semiconductors or metals but also direct bandgap semiconductors. This may be attributed to the difference contributions in the orbitals of each element to the total energy band between the parents and their corresponding Janus structures. Furthermore, by increasing alternative doping of Te atoms in SnS2 and SnSe2, the energy band can transform from indirect to direct bandgap semiconductors and then to metals. The tunable band structure makes Janus monolayer materials promising candidates for electronic device applications.