Effect of vacancies on structural, electronic and optical properties of monolayer MoS2: A first-principles study

Effects of vacancies on structural, electronic and optical properties of monolayer MoS2 were investigated using first-principles plane-wave pseudopotential method based on density functional theory. Results show that the band structure and band gap of perfect monolayer MoS2 are in good agreement with the available experimental and theoretical data. Structural analysis indicates that ions surrounding Mo vacancies show an outward relaxation, while that ions surrounding S vacancies exhibit slightly inward relaxation. Electronic analysis implies that the band gaps of defective monolayer MoS2 are smaller than that of perfect one. After introduction of neutral S-vacancy, monolayer MoS2 has changed from direct to indirect band gap. Mo vacancies bring about acceptor-like levels and p-type conductivities, whereas S vacancies lead to donor-like levels and n-type conductivities. With the increasing charge states of vacancies, the band gaps get smaller and the defect energy levels become deeper. Moreover, as the charge states of vacancies increase, the static dielectric constants of monolayer MoS2 with Mo vacancies decrease, whereas the static dielectric constants of monolayer MoS2 with S vacancies increase.