Ultrasharp Lateral p–n Junctions in Modulation-Doped Graphene

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We demonstrate ultrasharp (≲10 nm) lateral p–n junctions in graphene using electronic transport, scanning tunneling microscopy, and first-principles calculations. The p–n junction lies at the boundary between differentially doped regions of a graphene sheet, where one side is intrinsic and the other is charge-doped by proximity to a flake of α-RuCl 3 across a thin insulating barrier. We extract the p–n junction contribution to the device resistance to place bounds on the junction width. We achieve an ultrasharp junction when the boundary between the intrinsic and doped regions is defined by a cleaved crystalline edge of α-RuCl 3 located 2 nm from the graphene. Scanning tunneling spectroscopy in heterostructures of graphene, hexagonal boron nitride, and α-RuCl 3 shows potential variations on a sub 10 nm length scale. First-principles calculations reveal that the charge-doping of graphene decays sharply over just nanometers from the edge of the α-RuCl 3 flake.