Dry Transfer Process of Single-Layer Graphene on Multi-Layer Hexagonal Boron Nitride for High Quality Heterostructure

Carrier mobility of the graphene thin film is one of the most crucial factors to achieve superior device performance. Factors that influence the carrier mobility include film crystallinity, layer number, presence of contaminations, and effect of the substrate. In this work, to obtain high-quality graphene film, single-layer graphene film was formed on a hexagonal boron nitride (hBN) thin-film via mechanical exfoliation technique. Mechanical exfoliation of graphite was done on a silicon substrate covered with poly (methyl methacrylate)/ poly (acrylic acid). Three adjacent thin films, each having approximately 20 - 30 μm length and 3 - 4 μm width making an average area of 87.5 μm2 for each film. From the measured Raman spectrum, the 2D-to-G peak intensity ratio was 1.7, confirming that exfoliated graphene is a single layer. The absence of the D peak indicates minimum crystal defects in the film. The graphene layers were subsequently dry-transferred onto mechanically exfoliated multi-layer hBN thin film. The area of the exfoliated hBN is around 6,000 μm2. The quality of the transfer process was evaluated through inspection under an optical microscope. All three single-layer graphene thin films were successfully placed exactly on the hBN without any presence of bubble and wrinkle. The process was described very detailed. The formed single-layer graphene on hBN layer is expected to have superior electrical characteristics and can be utilized for the fabrication of high-performance nano device.