Characterization of graphene films and transistors grown on sapphire by metal-free chemical vapor deposition.

We present a novel method for the direct metal-free growth of graphene on sapphire that yields high quality films comparable to that of graphene grown on SiC by sublimation. Graphene is synthesized on sapphire via the simple decomposition of methane at 1425-1600 °C. Film quality was found to be a strong function of growth temperature. The thickness, structure, interface characteristics, and electrical transport properties were characterized in order to understand the utility of this material for electronic devices. Graphene synthesized on sapphire is found to be strain relieved, with no evidence of an interfacial buffer layer. There is a strong correlation between the graphene structural quality and carrier mobility. Room temperature Hall effect mobility values were as high as 3000 cm(2)/(V s), while measurements at 2 K reached values of 10,500 cm(2)/(V s). These films also display evidence of the quantum Hall effect. Field effect transistors fabricated from this material had a typical current density of 200 mA/mm and transconductance of 40 mS/mm indicating that material performance may be comparable to graphene on SiC.