Crucial Role of many-body van der Waals interaction in understanding the stability of point defects in MoS₂ monolayer

The present study investigates the stability of native point defects in MoS₂ monolayer by first-principles based approach under the framework of density functional theory (DFT). The property of band gap transition from indirect to direct on going from bulk to monolayer in MoS₂, establishes a huge potential in the optoelectronic industry. Defects being inevitable, their role in tuning the band gap for photovoltaics is an important approach. Initially, we have obtained the phase diagram that shows the most stable defect states with minimum Gibbs free energy of formation. We have considered charged and neutral states, of three vacancies and five antisites with the inclusion of many-body vdW interaction, which have posed a significant change in the stability pattern. The stable defect states as observed by HSE06 functional are, V_S (-2,+2), V_Mo (-2,+2), S_Mo (-2) antisite and S_2Mo (+2) antisite. They also have significant concentration at the finite temperature range of 50K-1000K, which is achieved by ab-initio atomistic thermodynamics along with the DFT input. Further, the S_Mo (-2) and S_2Mo (+2) antisites have tuned the band gap in the range 1.1 – 1.8 eV. These states have shown optical response in the visible region, hence increasing the absorption capability of MoS₂ monolayer.