First Principles Study on the Electronic Structure and Optical Properties of Graphene/MoS₂ Heterojunctions with Different Rotation Angles

Based on the density functional theory (DFT), first-principles calculations were performed to investigate the electronic structures and optical properties of graphene/MoS₂ heterostructures at several different twist angles. The results indicate that the twisted graphene/MoS₂ heterostructures still preserve some characteristics inherent in monolayer structure. Near the Fermi level, the characteristic linear dispersion band structure of graphene layer is retained, and the direct bandgap (E_g) at the Dirac cone is influenced by interlayer rotation modulation. The bandgap of MoS₂ layer exhibits a high sensitivity to layer thickness that the indirect bandgap continuously increases with the increase thickness. At a twist angle of 10.9°, the maximum value of E_g reaches 11.67 meV. The calculated differential charge density result indicates that with the interlayer rotations the Mo―S bond length is changed by the electron transfer between Mo and S atoms, resulting in a increasing of S-S interlayer distance. Simultaneously, the carrier concentration of graphene is increased when it forms a heterostructure with MoS₂. The rotation at the heterojunction interface increases the hole-doped carrier concentration to 9.2×10¹² cm⁻², approximately six times higher than that without twist angle. The results of the optical property calculations for the heterostructures indicate that at a twist angle of 27.0°, its absorption edge undergoes a redshift to the lower energy by 0.233 eV. At a twist angle of 10.9°, the absorption edge undergoes a blue shift, moving towards the higher energy by 0.116 eV. Within the visible light range, the loss function of graphene/MoS₂ heterostructure decreases by 0.007. This study can provide a theoretical basis for the design of new rotation graphene heterostructures optical nanodevices.