Density functional theory study the effects of point defects in β-In2S3

Using density functional theory calculations, the effects of point defects, including sulfur vacancy, indium vacancy, and niobium doping, on the crystal structure, electronic structure, and optical properties of β-In2S3 have been investigated. If the host contains the sulfur or indium vacancy, its band gap will be narrowed, while the niobium doping slightly broadens the band gap of β-In2S3. In the case of indium vacancy or niobium doping, the point defect introduces some impurity energy levels above the top of the valence band or below the bottom of the conduction band. These impurity energy levels could act as the intermediate band, which is used in the multi-photon absorption. Combined with the calculated results, accurate molecular orbital diagrams are proposed.