Effect of Vacancy on Electronic Properties of MX2 (M = Mo, W and X = S, Se) Monolayers

Two-dimensional transition metal dichalcogenides (TMDs), an emerging class of layered materials with promising optoelectronic properties, have become one of the most intensely studied nanomaterials for nanoelectronic and photonics applications. In this work, we studied the electronic properties of defective monolayer TMDs such as WS
₂
, WSe
₂
, and MoS
₂
by using first principle calculations based on density functional theory. We focused primarily on the effects of chalcogen vacancies on the electronic characteristics. We calculated their band structure, the density of states, effective mass, and mobility. Our first-principle calculations reveal that chalcogen vacancies induce non-zero density of states within the band gap. Hence, we found a significant decrease in the band gap when we introduced single chalcogen vacancies. For instance, the band gap of WS
₂
reduced from 1.8 eV to 0.79 eV. These defects modify the shape of the conduction and valence band and hence the notable increase in effective mass resulting in a decrease in mobility. The findings of this study provide an insight of defect engineering for modifying electronic properties, enhancing device performance, and enabling unique functionalities.