First-Principles Study on Optical Properties of Rare-Earth Doped Monolayer WTe₂ with Single Tellurium Vacancies

Based on first-principles calculations employing density functional theory with a planewave ultrasoft pseudopotential approach, we performed computations using the CASTEP (Cambridge Sequential Total Energy Package) module within the Materials Studio software. The electronic band structures, density of states, and optical properties of intrinsic monolayer WTe₂, monolayer WTe₂ with a single tellurium vacancy (V_Te), and rare-earth-doped V_Te-containing monolayer WTe₂ (V_Te-X, where X = Ce, Yb, Eu) were systematically investigated to explore the synergistic effects of rare-earth doping and tellurium vacancy defects on the optical properties of monolayer WTe₂. The results indicate that, compared to the V_Te model, the V_Te-X models lead to a more pronounced enhancement of the optical performance in the infrared region (0 eV– 1.2 eV). All V_TeX structures exhibit metallic characteristics, with a notable increase in the density of states near the Fermi level. In particular, the V_Te-Yb model demonstrates significant improvement in the infrared range: the absorption coefficient, reflectivity, static dielectric constant, and peak value of the imaginary part of the dielectric function are enhanced by factors of 3.76, 1.83, 2.63, and 24.20, respectively, compared to those of pristine monolayer WTe₂. This study provides a theoretical foundation for the design of infrared photodetectors based on monolayer WTe₂ substrates.