First-principles study of the electronic structure and optical properties of C-doped SnS₂.

Abstract

<h4>Context</h4>Density functional theory (DFT) was used to investigate the effects of varying carbon doping concentrations on the electronic and optical properties of SnS₂-doped systems. The findings show that a doping concentration of 3.7% in SnS₂ results in the highest structural stability and the lowest formation energy. A pure SnS₂ monolayer is an indirect bandgap semiconductor, and the result reveals that increasing carbon doping correlates with a gradual reduction in the system's bandgap. The density of states analysis reveals that the valence band comprises C-2p, S-3p, and Sn-5p orbitals, whereas the conduction band consists of S-3p, Sn-5 s, and C-2p orbitals. Furthermore, doping concentration appears to cause a redshift in both the absorption coefficient and reflection peaks, which both decrease as doping concentration increases.<h4>Methods</h4>The calculations for this study were performed using DFT within the CASTEP module of Materials Studio Segall et al. J Phys: Condens Matter 14(11):2717, 2002. The system parameters and structures were optimized to determine the electronic structure and optical properties. Geometric optimization and calculations were carried out with the generalized gradient approximation plane-wave pseudopotential method and the Perdew-Burke-Ernzerhof functional Perdew et al. Phys Rev Lett 80(4):891-891, 1998. The parameters for structural optimization included a plane-wave expansion cutoff energy set at 500 eV and a k-point mesh of 6 × 6 × 1 for Brillouin zone integration. The electronic convergence criteria were established at 1.0 × 10^-5 eV/atom for the unit cell energy and 1.0 × 10^-6 eV/atom for self-consistency. The internal stress deviation was maintained below 0.05 GPa, the atomic force interactions were kept under 0.03 eV/Å, and atomic displacements during geometric optimization were confined to less than 0.001 Å. To calculate the properties of the SnS₂ monolayer, a vacuum spacing of 15 Å along the z-axis was introduced to prevent interactions between adjacent layers.