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微細加工 名古屋大学 Nagoya University

Formation of a new nitride interface in epitaxial graphene on SiC

Wataru Norimatsu and Michiko Kusunoki, Nagoya University

 Kusunoki laboratory in Nagoya University developed a technique for obtaining graphene on the insulating substrate with a new nitride interface layer. 

 A one-atom-thin carbon material, graphene, has an extremely high carrier mobility, which raises hopes for next-generation semiconducting devices. Epitaxial graphene on SiC is the only method to obtain wafer-scale single-crystal graphene directly on the semi-insulating substrate. However, electrons in graphene on SiC are scattered by the phonon of the interfacial buffer layer, which results in the mobility decrease with increasing temperature. In this study, then, we challenged to form a novel interface layer by the nitrogen treatment.

 We first nitrided the surface of the semi-insulating SiC substrate by heating it at 1600C° in a nitrogen gas atmosphere. Then, the substrate was heated at 1700C° in an argon atmosphere to grow graphene.

 Figure (a) and (b) show the surface structure after nitridation. This structure has a new Si-N layer with a period of 4.6Å, between the 0th layer and SiC. This 0th layer has the same structure as the buffer layer which was present under normal epitaxial graphene on SiC. In the high-resolution transmission electron microscope image in (b), the area surrounded by a white rectangle is the simulated image, and it is in an excellent agreement with the experimental image, which supports the validity of the structural model shown in (a). After heating this substrate in an argon atmosphere, monolayer graphene was formed on this 0th layer with the nitride interface layer. The results of the Hall-effect measurement are shown in (c). The mobility decrease with increasing temperature was suppressed in graphene with a new nitride interface compared with the normal epitaxial graphene. This is explained by the reduced interfacial phonon scattering due to the new nitride interface layer. As a result, the mobility value at room temperature was improved.

 This work was published in "Physical Review B" (Y. Masuda, et al., Phys. Rev. B 91, 075421 (2015)).

Figure (a) Structural model of a nitride interface between the 0th layer and SiC. (b) High-resolution transmission electron microscope image of a nitride interface. The simulated image and the structural model are overlaid. (c) The electronic properties of graphene with a new nitride interface layer. Mobility and the electron concentration of graphene with a nitride interface and normal epitaxial graphene are shown as a function of temperature.