Probing top-gated field effect transistor of reduced graphene oxide monolayer made by dielectrophoresis

Abstract

We demonstrate a top-gated field effect transistor made of a reduced graphene oxide (RGO) monolayer (graphene) by dielectrophoresis. The Raman spectrum of RGO flakes of typical size of 5 µm × 5 µm shows a single 2D band at 2687 cm^-1, characteristic of single-layer graphene. The two-probe current-voltage measurements of RGO flakes, deposited in between the patterned electrodes with a gap of 2.5 µm using ac dielectrophoresis, show ohmic behavior with a resistance of ~37 kΩ. The temperature dependence of the resistance (R) of RGO measured between 305 K and 393 K yields a temperature coefficient of resistance [dR/dT] /R~-9.5 × 10^-4/K, the same as that of mechanically exfoliated single-layer graphene. The field-effect transistor action was obtained by electrochemical top-gating using a solid polymer electrolyte (PEO+LiClO₄) and Pt wire. The ambipolar nature of graphene flakes is observed up to a doping level of ~6 × 10¹²/cm² and carrier mobility of ~50 cm²/V s. The source-drain current characteristics show a tendency of current saturation at high source-drain voltage which is analyzed quantitatively by a diffusive transport model.