The influence of the band structure of epitaxial graphene on SiC on the transistor characteristics

We fabricated high-mobility field-effect transistors based on epitaxial graphene synthesized by vacuum graphitization of both the Si- and C-faces of SiC. Room-temperature field-effect mobilities >4000 cm²/V s for both electrons and holes were achieved, although with wide distributions. By using a high-k gate dielectric, we were able to measure the transistor characteristics in a wide carrier density range, where the mobility is seen to decrease as the carrier density increases. We formulate a simple semiclassical model of electrical transport in graphene, and explain the sublinear dependence of conductivity on carrier density from the view point of the few-layer graphene energy band structure. Our analysis reveals important differences between the few-layer graphene energy dispersions on the SiC Si- and C-faces, providing the first evidence based on electrical device characteristics for the theoretically proposed energy dispersion difference between graphene synthesized on these two faces of SiC.