Abstract:

Epitaxial graphene by chemical vapor deposition (CVD) is one of the main methods to fabricate high-quality wafer-scale graphene materials. However, CVD-grown graphene on metal substrates has some disadvantages, such as the need for a transfer process and carbon atoms dissolved into the metal substrate. In this work, we evaluate sapphire substrates to overcome those disadvantages. The morphology and crystal quality of the samples grown at different temperatures were characterized by atomic force microscopy (AFM), optical microscopy (OM), Raman spectroscopy, and a Hall measurement system. To ease the etching process of carbon atoms to the substrate, we adopt a very low carbon concentration of 0.01%. AFM and Raman results show that the surface morphologies of samples grown at lower temperatures were smoother, whereas the quality of samples grown at higher temperatures was better. The sapphire substrate was etched in an H₂ environment, while it was not etched only by carbon source without H₂ environment. Epitaxial graphene with flat surface morphology and good crystal quality was prepared on a c-plane sapphire substrate (diameter: 50 mm) at a growth temperature of 1200 ℃. The carrier mobility is above 1000 cm²·V^-1·s^-1 at room temperature.

Key words: Graphene, Sapphire, Chemical vapor deposition, Growth temperature, Etching mechanism