C-Plane Sapphire and Catalyst Confinement Enable Wafer-Scale High-Quality Graphene Growth

Herein we report a systematic study elucidating the role of H-2 in wafer-scale graphene synthesis on a Cu thin film using catalyst confinement (CC) and a C-plane sapphire substrate. Our process results in extremely flat and wrinkle-free graphene when coupled with a dry transfer process. The role of H-2 was investigated by variation of the H-2:CH4 flow ratio that, when optimized, was able to mitigate Cu catalyst roughening. This allows the Cu catalyst to maintain large monocrystalline grains extending several centimeters across growth wafers and predominantly in the Cu(111) orientation. The ultimate results are high-quality, continuous, and large-area graphene sheets. A comparison of graphene formation using the CC process with C-plane sapphire substrate and SiO2/Si wafers was conducted. The results highlight the benefits of using C-plane sapphire as substrates in contrast to SiO2/Si wafers on which highly roughened catalyst surfaces are usually formed leading to a high density of wrinkles in the graphene sheets as well as bilayer graphene growth at the Cu grain boundaries. Throughout the investigation, graphene quality was evaluated by Rainan spectroscopy and Cu catalyst orientation was determined by electron backscatter diffraction (EBSD). Graphene field effect transistors (GFETs) were fabricated to examine the electronic properties by transferring the graphene from the Cu/C-plane sapphire wafers and from Cu/SiO2/Si wafers to SiO2 substrates using a dry-transfer process developed in house. The CC and Cu/C-plane sapphire-based GFETs exhibit a charge carrier mobility as high as 3781 cm(2) V-1 s(-1).