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We have exploited conductive atomic force microscopy (CAFM) to characterize the vertical current transport from graphene (Gr) to the 2D electron gas of AlxGa1-xN/GaN heterostructures considering different kinds of AlGaN surfaces in terms of roughness and unevenness. The vertical current transport mechanism can radically change depending on these nanometer size superficial fluctuations whereby the nanoscale lateral resolution of CAFM current-voltage (IV) measurements offers the ideal conditions to distinguish this effect form the average macroscopic behavior. We have characterized bare and Gr-coated high quality AlGaN surface at first, observing for both a rectifying behavior. In particular the contact on Gr shows a lower Schottky barrier height (SBH)(ΦB= 0.4 eV) than the bare AlGaN (ΦB= 0.9 eV), and a smaller spread between the array of sampled positions. In particular this lateral homogeneity can be explained as an averaging effect of Gr on the AlGaN surface potential fluctuations over a length scale around the AFM tip in the order of the electron mean free path of a transferred CVD grown Gr (~ 100 nm). In order to exclude the role of the AFM metal tip force contact to the observed behavior we have performed a force dependent characterization establishing a tip force range in which this effect is negligible. We have also repeated the same characterizations on a Gr/AlGaN/GaN heterostructure with a high structured AlGaN surface. In this case a lower SBH (ΦB= 0.6 eV) and an ohmic behavior have been observed on bare AlGaN and Gr-coated AlGaN respectively. This result has been attributed to the presence of preferential current …
Science Publishing Group
Publication date: 
29 Jul 2015

Gabriele Fisichella, Giuseppe Greco, Patrick Fiorenza, Salvatore Di Franco, Fabrizio Roccaforte, Filippo Giannazzo

Biblio References: 
Volume: 1 Issue: 1 Pages: 1
Nanoscience and Nanometrology