Effect of graphene grain boundaries on MoS₂/graphene heterostructures

The grain boundaries of graphene are disordered topological defects, which would strongly affect the physical and chemical properties of graphene. In this paper, the spectral characteristics and photoresponse of MoS₂/graphene heterostructures are studied. It is found that the blueshift of the G and 2D peaks of graphene in Raman spectrum is due to doping. The lattice mismatch at the graphene boundaries results in a blueshift of MoS₂ features in the photoluminescence spectra, comparing to the MoS₂ grown on SiO₂. In addition, the photocurrent signal in MoS₂/hexagonal single-crystal graphene heterostructures is successfully captured without bias, but not in MoS₂/polycrystalline graphene heterostructures. The electron scattering at graphene grain boundaries affects the optical response of MoS₂/graphene heterostructures. The photoresponse of the device is attributed to the optical absorption and response of MoS₂ and the high carrier mobility of graphene. These findings offer a new approach to develop optoelectronic devices based on two-dimensional material heterostructures.