title: Ballistic bipolar junctions in chemically gated graphene ribbons.
abstract: The realization of ballistic graphene pn-junctions is an essential task in order to study Klein tunneling phenomena. Here we show that intercalation of Ge under the buffer layer of pre-structured SiC-samples succeeds to make truly nano-scaled pn-junctions. By means of local tunneling spectroscopy the junction width is found to be as narrow as 5 nm which is a hundred times smaller compared to electrically gated structures. The ballistic transmission across the junction is directly proven by systematic transport measurements with a 4-tip STM. Various npn- and pnp-junctions are studied with respect to the barrier length. The pn-junctions are shown to act as polarizer and analyzer with the second junction becoming transparent in case of a fully ballistic barrier. This can be attributed to the almost full suppression of electron transmission through the junction away from normal incidence.
authors.affiliation: Institut für Festkörperphysik, Leibniz Universität Hannover, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Baringhaus
authors.affiliation: Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Stöhr
authors.affiliation: Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany.
authors.forename: Stiven
authors.initials: S
authors.lastname: Forti
authors.affiliation: Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Starke
authors.affiliation: Institut für Festkörperphysik, Leibniz Universität Hannover, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Tegenkamp