Comparison of Epitaxial Graphene on Si-face and C-face 6H-SiC
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Comparison of Epitaxial Graphene on Si-face and C-face 6H-SiC Shin Mou1, J. J. Boeckl1, L. Grazulis1, B. Claflin2, Weijie Lu3, J. H. Park1, and W. C. Mitchel1 1 Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, OH 45433, USA 2 Wright State University, Semiconductor Research Center, Dayton, OH 45435, USA 3 Fisk University, Department of Chemistry, Nashville, TN 37208, USA ABSTRACT We present atomic force microscopy (AFM), Hall-effect measurement, and Raman spectroscopy results from graphene films on 6H-SiC (0001) and (000-1) faces (Si-face and Cface, respectively) produced by radiative heating in a high vacuum furnace chamber through thermal decomposition. We observe that the formation of graphene on the two faces of SiC is different in terms of the surface morphology, graphene thickness, Hall mobility, and Raman spectra. In general, graphene films on the SiC C-face are thicker with higher mobilities than those grown on the Si-face. INTRODUCTION Graphene, which consists of a few layers of atomic carbon sheets, has recently attracted great interests thanks to its unique electronic and optical properties such as very high mobility and optical transparency. To produce graphene, there are several methods including mechanical exfoliation discovered by Novoselov and Geim et al. in 2004 [1], which allows for investigation of the electronic properties of graphene. Due to the limited size of graphene flakes generated by this method (maximum size about 1 mm2), other methods have been adapted for applications which require wafer-size graphene films such as epitaxial graphene grown by SiC sublimation [2, 3], metal-catalyst CVD growth [4, 5], and direct carbon deposition [6, 7]. Among these, epitaxial graphene has been proven to produce high quality and highly uniform graphene across the SiC substrate and is also ready for photolithography fabrication with no physical transfer required. Therefore, it is currently the preferred material for high-speed and high-performance graphene field effect transistor (GFET) [8, 9]. It was long known in the SiC community that annealing SiC at high temperatures resulted in the sublimation of Si and the formation of a graphite-like carbon layer on the SiC surface [10], but it was not until Berger et al. [2] conducted thermal decomposition of SiC in ultra high vacuum (UHV) to produce ultra-thin graphite (graphene) on the SiC Si-face that it became an important electronic material. Emtsev et al. [3] later demonstrated high quality growth of the Siface graphene by decomposition of SiC in atmospheric pressure argon ambient. However, despite the good uniformity of the thickness and the atomic flatness of graphene on the SiC Siface, the reported Hall mobilities of the ungated graphene are on the order of 1000 cm2/Vs [11] – lower than those of exfoliated graphene. On the other hand, graphene grown on the SiC C-face has been reported with Hall mobility values of more than 10,000 cm2/Vs [11]. Nonetheless, thickness uniformity, film stacking, and surface morpholo
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