Understanding and Controlling Vanadium Doping and Sulfur Vacancy Behavior in Two-Dimensional Semiconductors: Toward Predictive Design

Doping in transition-metal dichalcogenide (TMD) monolayers provides a powerful method to precisely tailor their electronic, optical, and catalytic properties for advanced technological applications, including optoelectronics, catalysis, and quantum technologies. However, the doping efficiency and outcomes in these materials are strongly influenced by the complex interactions between introduced dopants and intrinsic defects, particularly sulfur vacancies. This coupling between dopants and defects can lead to distinctly different behaviors depending on the doping concentration, presenting significant challenges in the predictable and controlled design of TMD properties. For example, in this work we systematically varied the p-type vanadium(V) doping density in tungsten disulfide (WS₂) monolayers and observed a transition in doping behavior. At low concentrations, V-dopants enhance the native optical properties of WS₂, as evidenced by increased photoluminescence, without introducing new electronic states. However, at higher concentrations, V-dopants promote the formation of vanadium-sulfur vacancy complexes that generate midgap states, with energies that can be precisely tuned by controlling the vanadium concentration. Using a combination of excitation- and temperature-dependent photoluminescence microscopy, atomic-resolution scanning transmission electron microscopy, and first-principles calculations, we identify attractive interactions between p-type V-dopants and n-type monosulfur vacancies. Our results provide a mechanistic understanding of how enthalpic dopant-defect interactions versus entropic effects govern the balance between property enhancement and perturbation of TMDs and suggest a pathway toward the rational design of doping strategies for next-generation optoelectronic, catalytic, and quantum devices.