First-principle studies of monolayer and bulk InSe1−xSx

Abstract

S-substitution doped monolayer and bulk InSe exhibit opposite bandgap behaviors. The bandgap in the monolayer InSe1−xSx (x = 0, 0.125, 0,25) decreases with increasing S concentration. However, the bandgap in bulk InSe1−xSx increases with the increase of S concentration. It is mainly because In, and Se(S) at the Fermi level have different strengths of bonding and anti-bonding states. In addition, the first-neighbor interatomic force constant (IFC) of the dopant atom S is higher than that of Se. The enhanced IFC in bulk InSe1−xSx corresponds to the Raman spectral blueshift phenomenon observed in earlier experiments. The electro-acoustic interactions of the material are strongly correlated with dimensionality, which leads to differences in optical properties between monolayer and bulk InSe1−xSx. The optical dielectric functions indicate that monolayer and bulk InSe1−xSx can be applied in different fields. Substitutional doping could modulate pz-like orbital interactions, which provides clues for modulating the electronic orbital structure of InSe materials for optoelectronic and optical applications.