Ballistic transport of graphene pnp junctions with embedded local gates

Abstract

We fabricated graphene pnp devices, by embedding pre-defined local gates in an oxidizedsurface layer of a silicon substrate. With neither deposition of dielectric material onthe graphene nor electron-beam irradiation, we obtained high-quality graphenepnp devices without degradation of the carrier mobility even in the local-gateregion. The corresponding increased mean free path leads to the observation ofballistic and phase-coherent transport across a local gate 130 nm wide, whichis about an order of magnitude wider than reported previously. Furthermore,in our scheme, we demonstrated independent control of the carrier density inthe local-gate region, with a conductance map very much distinct from those oftop-gated devices. This was caused by the electric field arising from the global backgate being strongly screened by the embedded local gate. Our scheme allows therealization of ideal multipolar graphene junctions with ballistic carrier transport.