Back-gate graphene field-effect transistors with double conductance minima

The Dirac cone structure of the energy band of the single-layer graphene gives rise to ambipolar conduction which results from the conversion of the conductive carriers in graphene between electrons and holes under the effect of the electrical field. Therefore, the graphene field-effect transistor (GFET) exhibits a V-shaped transfer characteristic curve with an electron and hole conduction branch converting at a conductance minimum. However, in this paper, unique W-shaped σ–Vg curve with double conductance minima instead of the typical V-shaped one is observed in GFET based on chemical vapor deposition grown graphene, demonstrating a graphene p–n junction behavior. The observation is not expected from the energy band structure of graphene and probably results from the doping effect of the metal contact on the underlying graphene, which leads to a misalignment of the Fermi level between graphene under the metal contact and in the channel area, and ultimately induces the double conductance minima because of the formation of the graphene p–n junction.