Characteristics of solution gated field effect transistors on the basis of epitaxial graphene on silicon carbide

A solution gated field effect transistor has been fabricated on epitaxial single-layer graphene on 6H-SiC(0 0 0 1). Output and transfer characteristics were systematically studied as a function of electrolyte pH. The transfer characteristics of the device show a pH dependent shift of 19 +/- 1 mV/pH. From the minimum sheet conductivity observed, an average charge carrier mobility of 1800 +/- 100 cm(2) V(-1) s(-1) at room temperature has been inferred. It turns out that the Fermi level in the graphene layer is strongly pinned in the vicinity of the Dirac point. The analysis of the transfer characteristics is consistent with a concentration of 4 x 10(14) cm(-2) interface states at 0.1 eV below the Dirac energy that is presumably associated with the (6 root 3 x 6 root 3)R30 degrees-reconstruction at the interface between SiC(0 0 0 1) and graphene.