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TT: Fachverband Tiefe Temperaturen

TT 78: Graphene: Electronic Properties (organized by O)

TT 78.2: Vortrag

Mittwoch, 2. April 2014, 16:15–16:30, WIL C107

Transport in chemically gated graphene p-n junctions — •Jens Baringhaus¹, Alexander Stöhr², Ulrich Starke², and Christoph Tegenkamp¹ — ¹Leibniz Universität Hannover, Institut für Festkörperphysik, 30167 Hannover, Germany — ²Max-Planck Institut für Festkörperforschung, 70569 Stuttgart, Germany

The chirality of charge carriers in graphene allows them to get through potential barriers without any reflection (known as Klein tunneling). To study this effect the fabrication of well-defined p-n junctions is necessary. We use the intercalation of Ge to convert the buffer layer on the SiC(0001) surface into graphene with local p-type or n-type doping depending on the local Ge coverage. The buffer layer is initially patterned using optical lithography, to fabricate isolated n-p, n-p-n and p-n-p structures. The n- and p-type doping (340 meV, -290 meV) is confirmed by STS which also reveals very narrow p-n junctions with a length below 5 nm. The corresponding electric fields are as high as 10⁶ V/cm and therefore significantly higher than those induced by field effects, providing a perfect environment to study Klein tunneling. Transport experiments are carried out by means of a 4-tip STM system, on n-p-n as well as p-n-p structures. Their resistance was found to be strongly dependent on temperature and the inner barrier length. While short barriers (< 200 nm) appear almost transparent, the resistance increases rapidly for barrier widths exceeding the coherence length (> 600 nm). The resistance of a single p-n junction fits to the theoretically predicted value for a Klein tunneling junction.