Unveiling the Electronic and Optoelectronic Properties of Pure, Point-Defective, and Isovalent Ru-Doped OsI₂ Monolayer: Defect Recovery from First Principles

In this paper, we report the effects of point defects and doping on the physical properties of the two-dimensional OsI₂ monolayer. A point defect was created by removing a single Os/I atom from the perfect crystal lattice of the OsI₂ monolayer. For doping, we use an isovalent Ru element from the transition-metal family. Point defects and doping alter the band structure by creating new localized electronic states within the gap. Moreover, the electronic bands show a shift due to point defects. However, changes in the bandgap due to point defects and doping are not remarkable. This suggests that isovalent Ru doping is favorable in the OsI₂ crystal lattice for the formation of other similar hybrids. Moreover, the isoelectronic substitution of the Ru atom at the Os vacancy contributes to defect recovery. The dielectric and optical properties of the point-defect OsI₂ monolayer change significantly at low energies. For instance, the dielectric function abruptly changes in the infrared (IR) region in the presence of the Os and I vacancies, significantly altering the optical absorption. A sudden increase in the dielectric constant increases the material’s refractive index (4.04), which is slightly greater than that of silica (3.9). The obtained reflection and transmission spectra demonstrate that these materials are potential candidates for anti-reflective coatings, as they exhibit reflectivity below 25% across the IR, visible, and ultraviolet regions. The pure and Ru-doped materials exhibit excellent static reflectivity below 4%, whereas the defective OsI₂ monolayers exhibit reflectivity below 6%. Furthermore, all the optical responses in these materials are polarization-dependent, indicating anisotropic behavior under the incident light field. The observations in this work show that these are excellent anisotropic optical materials with potential for use in optical instruments and optoelectronic device applications.