By embedding pre-defined poly silicon local gates in an oxidized surface layer of a silicon substrate, the team has obtained clean pnp junctions without any dielectric material deposition nor electron beam exposure on the surface of the graphene sheet. The scheme allows scientists to observe ballistic and phase-coherent transport in the device across a 130 nm-wide local gate. According to the group, this is much wider than the range of phase coherence ever reported.

With local gates imbedded inside the substrate, the device structure can be further improved by adopting a variety of methods for enhancing the mobility in graphene, such as Ar/H2 annealing or transference onto boron-nitride substrates. The fabrication scheme enables the study of graphene pnp junctions in a fully ballistic regime, where it may be possible to observe many novel phenomena such as Veselago lensing. The method will also facilitate scanning-tunneling-spectroscopic studies on graphene pn boundaries, without dielectric coverage, to probe the details of scattering and/or tunneling processes as well as the existence of snake states in finite magnetic fields.

Further details can be found in the journal Nanotechnology.