S-Vacancy induced indirect-to-direct band gap transition in multilayer MoS2

Abstract

Two-dimensional (2D) MoS₂ has various potential applications due to its attractive band gap of 1.29–1.90 eV and unique photoelectric properties. Furthermore, it is well-known that multilayer and bulk MoS₂ structures possess an indirect band gap. In this paper, however, our first-principles calculations demonstrated that the creation of S vacancies in the multilayer and bulk MoS₂ structures can achieve indirect-to-direct band gap transition, leading to a decrease in the band gap energies from 0.984–1.542 eV to 0.629–0.971 eV. Although the generation of Mo vacancies cannot cause such indirect-to-direct band gap transition, the Mo vacancies also decrease the band gap energies of the multilayer and bulk MoS₂ structures to 0.369–0.460 eV. Furthermore, the band gap energy of the vacancy-defected multilayer MoS₂ decreases with the increasing number of layers. Optical properties are also remarkably affected by atomic vacancies, that is, the absorption edges in the defect structures of MoS₂ present a redshift and significantly enhance the visible light absorption compared to the corresponding pristine structures. These findings provide a novel approach to tuning the electronic structure and dielectric properties of MoS₂ for specific future applications.