VLS Growth of III-V Semiconductor Nanowires on Graphene Layers
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VLS Growth of III-V Semiconductor Nanowires on Graphene Layers K. Tateno*1, D. Takagi1, G. Zhang1, H. Gotoh1, H. Hibino1 and T. Sogawa1 1 NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato- Wakamiya, Atsugi, Kanagawa 243-0198, Japan. ABSTRACT GaP, GaAs, and InP nanowires were grown on graphitic layers by the vapor-liquid-solid method in a metalorganic vapor phase epitaxy chamber. On graphene/SiC(0001), Au particles as catalyst were formed at the steps by controlling the Au deposition rate and the annealing temperature in a low-energy electron microscopy system. GaP nanowires were grown on this substrate, and it was found that vertical nanowires were formed at the steps of the surface. We also performed GaP, GaAs, and InP nanowire growth on graphite substrates. Free-standing nanowires were obtained for all three materials, although they were vertically, diagonally, and laterally-oriented at the same time. The results suggested that the growth at the steps is the key to growing nanowires vertically on graphene surface. INTRODUCTION Graphene has attracted considerable interest as a new material for high-speed devices because its carrier mobility exceeds 200,000 cm2V-1s-1, the highest among materials [1]. Recently, the large-scale growth of single-layer and few-layer graphene has been demonstrated, and the advanced technique of transferring graphene sheets to flexible plastic substrates has led to stretchable, foldable, and transparent electronics and optoelectronics [2]. The growth of inorganic semiconductor nanodevices on graphene sheets will be one of the promising techniques for future device application. There have been several reports on semiconductor nanostructures grown on graphene layers [3-5]. Kim et al. reported ZnO nanowires grown on few-layer graphene on SiO2. They showed an apparent difference between nanowire growth on graphene and that on the SiO2: straight and vertical ZnO nanowires were grown on the graphene region, while randomly oriented ones were grown on the SiO2 region [3]. They attributed the success of the epitaxy on grapene to the similar hexagonal atomic configuration in the c plane of both materials, although their a-axis lattice constants are quite different (aZnO = 3.249 Å for ZnO and agraphene = 2.461 Å for graphene) [4]. Hong et al. reported the growth of GaAs and InAs on graphite surface with artificially formed monomolecular layer ledges or kinks by catalyst free metal-organic vapor phase epitasy (MOVPE). They were able to grow nanowires for InAs, but only islands were yielded for GaAs along the step-edges of the graphitic layers. They discussed the nanowire growth on graphene as noncovalent heteroepitaxy, which is called van der Waals epitaxy [6]. The point is that nearly coherent in-plane lattice matching (misfit of 0.49%) between InAs and the graphitic surface plays a critical role in the epitaxial formation of vertical InAs nanowires, whereas the large misfit of 6.22% for GaAs leads to island morphologies. Although this reasoning is similar to that of Kim et al., the c
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