Engineering of Vacancy Defects in WS2 Monolayer by Rare-Earth (Er, Tm, Lu) Doping: A First-Principles Study

Vacancy defects in two-dimensional (2D) materials are critical to their properties. The substitutional doping in vacancy defects by rare-earth atoms results in diverse material versatilities, but the effects and the corresponding mechanisms are far from being answered. Herein, the electronic and optical properties of vacancy defects and lanthanide rare-earth (RE = Er, Tm, Lu) doping in WS2 monolayers are studied based on density functional theory with Hubbard correction (DFT + U). The formation energies of defective and doped systems are calculated under W-rich and S-rich conditions, respectively. The bandgap of WS2 with one W-defect in a 4 x 4 x 1 supercell changes from direct to indirect, while S-defect does not change the bandgap type of the supercell. When RE atoms are doped in the W-defect, the bandgap returns to direct. WS2 supercells with intrinsic defects and Lu doped in [W] defect show the nonmagnetic property, while Er- and Tm-doped supercells show obvious magnetic properties. The imaginary part of dielectric function and absorption coefficients increase drastically from visible to near-infrared as RE atoms substitute W sites, and the bandgap shrinks due to the rise of the valance band maximum. This work proves RE doping in 2D WS2 is an effective technique for bandgap and carrier engineering.