MOCVD of WSe2 crystals on highly crystalline single- and multi-layer CVD graphene

The scalable synthesis of van der Waals vertical heterostructures (vdWHs) is viewed as an important milestone for the fabrication of novel 2D-based functional applications. Combining semi-metallic graphene with semiconducting transition metal dichalcogenides (TMDs) shows great potential to explore new device architectures with unique functionalities. In this work, we investigate the gas-source metal–organic chemical vapor deposition (MOCVD) of tungsten selenide (WSe₂) on highly crystalline CVD graphene. Single- and multi-layer graphene constitute interesting testing grounds for investigating fundamental WSe₂ growth mechanisms owing to its atomically smooth surface, absence of dangling bonds, chemical inertness, and hexagonal lattice symmetry. Our experimental results show how the graphene template properties influence the WSe₂ nucleation site density, growth rate, in-plane orientation, and thickness. In particular, we found that WSe₂ growth behavior strongly depends on the number of graphene layers, their stacking order/twisting angle, as well as on the nature of the substrate underneath.