The first-principles study on the halogen-doped graphene/MoS₂ heterojunction

Monolayer graphene has a zero band gap, and monolayer MoS₂ has a direct band gap of 1.80 eV. In the form of van der Waals heterostructure, the combination can open the Dirac point of graphene. In this paper, the graphene/MoS₂ heterojunctions were doped with the elements of F, Cl, Br and I to construct four systems. The defect formation energies, electronic structures and optical properties of four doped systems were calculated based on the first-principles. According to the defect formation energies, S vacancy became the best choice of doping site. The band structures of the doped heterojunctions changed significantly and appeared new energy levels. In addition, the MoS₂ layers in the four heterojunctions produced some density of states near the Fermi surface. By calculating the optical properties that are the dielectric functions of the four halogen-doped graphene/MoS₂ heterojunctions, the optical absorption range of the halogen-doped heterojunctions expanded from the visible light range to the infrared light range. This phenomenon indicates that the doping of halogen in the graphene/MoS₂ heterojunction can expand the light absorption range of the heterojunction and improve the utilization rate of the heterojunction to infrared light.