Catalytic mechanisms and contamination effects of metal catalysts in the direct growth of graphene on silicon substrates

Direct growth of graphene films on non-catalytic substrates, such as silicon (Si), remains challenging due to the absence of catalytic activity for carbon source decomposition. The additional metal catalysts were introduced to overcome this limitation, their vapor pressure and catalytic ability could strongly affect the catalytic efficiency and impurity level of fabricated graphene films. In this study, the catalytic mechanisms and contamination effects of different catalysts in the direct growth of graphene on Si substrates by CVD were investigated. Methane decomposition process occurred on the catalysis surface was calculated with volumetric methane concentration model, while carbon radical diffusion process in the CVD chamber was simulated by FEA Multiphysics Modelling. The predicted methane decomposition efficiencies were approximately 100 %, 0.48 %, and 0.08 % for Ni, Cu, and Ga foils under 300 sccm carrier gas at atmosphere, respectively. The results indicated Ni catalyst exhibited the highest methane decomposition efficiency. Graphene synthesized with the Ni catalyst exhibited good crystallinity, low defect density, and low sheet resistance. XPS analysis indicated the absence of catalyst contamination under Ni catalyzation, while SEM-EDS re-confirmed no detectable Ni contamination in the fabricated graphene. In contrast graphene grown with Cu or Ga catalysts exhibited obvious metal contamination. Our work suggested that metal with high catalytic ability and low vapor pressure will be more favourable for uniform, good crystallinity and non-contamination graphene films directly growth on silicon substrate.