Synthesis of large-area multilayer hexagonal boron nitride for high material performance

Although hexagonal boron nitride (h-BN) is a good candidate for gate-insulating materials by minimizing interaction from substrate, further applications to electronic devices with available two-dimensional semiconductors continue to be limited by flake size. While monolayer h-BN has been synthesized on Pt and Cu foil using chemical vapour deposition (CVD), multilayer h-BN is still absent. Here we use Fe foil and synthesize large-area multilayer h-BN film by CVD with a borazine precursor. These films reveal strong cathodoluminescence and high mechanical strength (Young's modulus: 1.16+/-0.1 TPa), reminiscent of formation of high-quality h-BN. The CVD-grown graphene on multilayer h-BN film yields a high carrier mobility of ~24,000 cm² V^-1 s^-1 at room temperature, higher than that (~13,000 ² V^-1 s^-1) with exfoliated h-BN. By placing additional h-BN on a SiO₂/Si substrate for a MoS₂ (WSe₂) field-effect transistor, the doping effect from gate oxide is minimized and furthermore the mobility is improved by four (150) times.