Dresden 2014 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 76: Graphene: Electronic properties (organized by O)
HL 76.2: Talk
Wednesday, April 2, 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.