Ab-initio investigation of optoelectronic properties for Pb doped MoSe2 using GGA+U approach: Band gap engineering

The GGA+U method of density functional theory has been systematically applied to the study of the structural, electronic and optical properties of Pb-doped MoSe 2 in bulk and slab systems. The stability of the Pb incorporation into the MoSe 2 lattice is verified by the use of structural optimization. The calculated electronic band structures reveal that doping strongly narrows the band gap, producing narrow-gap semiconducting or nearly gapless behavior rather than a strictly metallic state. The small but finite band gaps, ranging from 0.018 to 0.267 eV, indicate quasi-metallic-like electronic characteristics, which may support enhanced carrier transport at finite temperature while preserving a residual semiconducting gap. According to the density of states analysis, the dominance of Se-p and Mo-d orbitals around the Fermi level, and the introduction of impurity states by Pb which increases carrier density. Pb doping has a strong influence on optical response and visible and ultraviolet absorption are highly visible. The imaginary component of the dielectric function contains clear peaks of the imaginary at about 2.0 eV (spin-up) and 0.4 eV (spin-down), which are interband transitions. The slab design has lower reflectivity (approximately 5% at 8.2 eV) and a higher number of surface-related optical features, reflecting better transparency in the ultraviolet region. This work is novel since it has comparatively studied the bulk and slab geometries of Pb-doped MoSe 2 with GGA + U and has demonstrated the importance of dimensionality and the state caused by impurities in the tuning of electronic structure, and optical performance. These results indicate that Pb doping is a viable pathway to customize MoSe 2 to be used in optoelectronic, photonic and transparent device technologies.