Electronic transport properties of top-gated monolayer and bilayer graphene devices on SiC
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Electronic transport properties of top-gated monolayer and bilayer graphene devices on SiC Shinichi Tanabe, Yoshiaki Sekine, Hiroyuki Kageshima, Masao Nagase†, and Hiroki Hibino NTT Basic Research Laboratories, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan † Present address: The University of Tokushima, 2-1 Minamijosanjima, Tokushima 770-8506, Japan ABSTRACT We studied the electronic transport properties of monolayer and bilayer graphene in topgated geometries. Monolayer and bilayer graphene were epitaxially grown by thermal decomposition of SiC. The half-integer quantum Hall effect under the gated environment was observed in monolayer graphene devices. The mobility of the monolayer and bilayer graphene devices showed distinct characteristics as a function of carrier density, which reflect their electronic structures. Strong temperature dependence at the charge neutrality point was observed in bilayer graphene devices, suggesting band gap opening. INTRODUCTION Monolayer and bilayer graphene have gained significant attention because of their intriguing physical properties [1]. For example, the high mobility in monolayer graphene suggests that it might be useful as a future electronics material [2]. Due to the zero band gap characteristic of monolayer graphene, however, a high on/off ratio cannot be expected, which is a major obstacle to making monolayer-graphene-based logic devices. Therefore, monolayer graphene is more suited for high frequency analog applications rather than for digital electronics applications. On the other hand, a band gap opens in bilayer graphene when a potential difference between the two layers is induced [3, 4]. The band gap opening was confirmed experimentally by angle-resolved photoelectron spectroscopy (ARPES) in a bilayer graphene formed on a SiC substrate, where a potential asymmetry was induced by electron doping from the substrate [5]. This makes bilayer graphene a candidate for logic applications. The mechanical exfoliation of graphite is a common way of making graphene because high-quality graphene can be obtained [6]. However, this technique is only good for making graphene flakes of only a few tens micrometers in size. For industrial applications of graphene, an alternative method that can produce high-quality graphene on a large scale is necessary. The epitaxial growth of graphene by thermal decomposition of SiC [7] and by chemical vapor deposition (CVD) [8] has been shown to yield graphene on a large scale. If we use CVD, the graphene has to be grown on a metal surface and then transferred to an insulating substrate. In contrast, if graphene is grown on SiC with the proper resistivity, the graphene does not need to be transferred because the substrate itself acts as an insulator. Graphene grown on the Si face of SiC also gives better control of few-layer graphene growth. Monolayer and bilayer graphene can be grown to large scales in Ar atmosphere [9] and in an UHV environment [10, 11], respectively, on the Si face of SiC. In both cases, the number of grown graphene l
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