Tuning the electronic and optical properties of ZnO through sulfur doping: A DFT study

This work presents a first-principles investigation of the structural, electronic, and optical properties of sulfur-doped ZnO_1-xS_x alloys using density functional theory. Starting from wurtzite ZnO, we systematically substituted oxygen with sulfur over the full composition range, generating relaxed structures that exhibit gradual lattice expansion consistent with the larger ionic radius of S²⁻. The electronic band gap displays a clear non-monotonic evolution as a function of sulfur content. The optical properties are systematically analyzed across the entire sulfur composition range (0 ≤ x ≤ 1), providing a comprehensive picture of composition-dependent dielectric response and light absorption in ZnO_1-xS_x alloys. Simulation results show that sulfur incorporation dramatically enhances the dielectric response and optical absorption in the visible range, with the strongest enhancement occurring at intermediate S concentrations (around 37.5–50%). At higher S contents, the absorption edge shifts back toward the ultraviolet, following the widening of the band gap. Together, these results highlight sulfur substitution as an effective strategy for engineering the band structure and optical response of ZnO, enabling the design of ZnO_1-xS_x alloys with tunable properties for optoelectronic, photovoltaic, and photocatalytic applications.