Lateral uniformity of the transport properties of graphene/4H-SiC (0001) interface by nanoscale current measurements
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1205-L03-02
Lateral uniformity of the transport properties of graphene/4H-SiC (0001) interface by nanoscale current measurements F. Giannazzo1, S. Sonde1,2, J.-R. Huntzinger3, A. Tiberj3, R. Yakimova4, V. Raineri1 and J. Camassel3 1
CNR –IMM, Strada VIII, 5, 95121, Catania, Italy Scuola Superiore di Catania, Via San Nullo, 5/I, 95123, Catania, Italy 3 GES, CNRS and Université Montpellier 2, 34095 Montpellier cedex 5, France 4 IFM, Linkoping University, Linkoping, Sweden 2
ABSTRACT Conductive Atomic Force Microscopy was applied to study the lateral uniformity of current transport at the interface between graphene and 4H-SiC, both in the case of epitaxial graphene (EG) grown on the Si face of 4H-SiC and in the case of graphene exfoliated from HOPG and deposited (DG) on the same substrate. This comparison is aimed to investigate the role played by the C-rich buffer layer present at EG/4H-SiC interface and absent in the case of DG/4H-SiC. The distribution of the local Schottky barrier heights at EG/4H-SiC interface (ΦEG) was compared with the distribution measured at DG/4H-SiC interface (ΦDG), showing that ΦEG (0.36±0.1eV ) is ∼0.49eV lower than ΦDG (0.85 ± 0.06eV). This difference is explained in terms of the Fermi level pinning ∼0.49eV above the Dirac point in EG, due to the presence of positively charged states at the interface between the Si face of 4H-SiC and the buffer layer. INTRODUCTION Graphene is currently the object of many experimental and theoretical studies [1,2], due to its outstanding transport properties, making this material a promising candidate for post-Si electronics. Most of experiments have been carried out on graphene obtained by mechanical exfoliation of highly oriented pyrolityc graphite (HOPG). In fact, this is the easiest and quickest method to obtain graphene sheets of very high crystalline quality, which can be deposited on several materials. The obtained flakes are typically small (from 1×1 to 100×100 µm2) and the yield of production is extremely low. This makes the method not suitable for applications. Another recently demonstrated method is solid-state graphitization of SiC [3-5]. It allows production of epitaxial graphene (EG) at the wafer scale and shows better prospects for longterm industrial applications. EG is obtained from high temperature thermal treatments performed either in ultra-high-vacuum or in standard secondary vacuum or, even, at atmospheric pressure in an inert gas atmosphere. Both the (0001) Si face and (000-1) C face of hexagonal SiC polytypes (4H and 6H) have been used but large differences have been found in the structural and electronic properties of EG grown on the two faces [6,7]. In particular, EG synthesis on the (0001) face of SiC occurs through a series of complex surface reconstructions. The precursor of graphene formation is a carbon-rich layer with (6√3×6√3)R30° reconstruction. This is not yet a real graphene layer but, simply, a buffer layer with a large percentage of sp2 hybridization and covalently bonded to the substrate [7]. The first real graphene
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