First-principles study of intrinsic point defects in monolayer SnS

The electronic and optical properties of two-dimensional materials are strongly affected by the presence of defects. In this study, we systematically investigated the influence of intrinsic point defects on the structural, electronic and optical properties of SnS monolayers using density functional theory. The intrinsic point defects such as vacancies, interstitials and antisites were analysed to map their defect energetics and electronic activity. Electronic structure analysis reveals that the pristine SnS monolayer shows semiconducting behaviour with an indirect band gap of1.42eV. The introduction of defects modifies the electronic band structure with the creation of mid-gap states and the shift of the Fermi level. Optical property calculations reveal that the presence of defect states strongly perturbs the dielectric functions. A red-shift in the absorption edge is observed due to defect induced mid-gap states. Under S-poor conditions, neutral sulphur vacancies (VS0) are thermodynamically more favourable than other defects. Negatively charged Sn vacancies (VSn-1) become energetically preferred under S-rich conditions, thus they are expected to form spontaneously. Our calculated results provide essential insights for defect engineering of SnS monolayers for future optoelectronic and photovoltaic applications.