Wide-Gap Semiconducting Graphene from Nitrogen-Seeded SiC

Abstract

All carbon electronics based on graphene has been an elusive goal. For more than a decade, the inability to produce significant band-gaps in this material has prevented the development of graphene electronics. We demonstrate a new approach to produce semiconducting graphene that uses a submonolayer concentration of nitrogen on SiC sufficient to pin epitaxial graphene to the SiC interface as it grows. The resulting buckled graphene opens a band-gap greater than 0.7eV in the otherwise continuous metallic graphene sheet. The goal of developing all-carbon electronics requires the ability to dope graphene and convert it between metallic and wide band-gap semiconducting forms. While doping graphene by adsorbates or more elaborate chemical means has made rapid progress, 1-7 opening a band-gap in graphene has been problematic. Two routes to wide-band-gap semiconducting graphene have been pioneered: electron confinement and chemical functionalization. Electron confinement in lithographically patterned narrow graphene ribbons has been plagued by lithographic limits and edge disorder, 8-11 although recent results from sidewall grown graphene ribbon are showing new progress that could lead to band-gaps larger than 0.6eV. 12,13 Functionalized graphene band-gaps can be produced by imposing a periodic potential in the graphene lattice through ordered adsorbates 14,15 or ordered impurities replacing carbon atoms. 16 In this work we demonstrate a novel approach to bandgap engineering in graphene using a nitrogen seeded SiC surface. Rather than using chemical vapor deposition (CVD) or plasma techniques to dope graphene by post seeding the films with nitrogen, 5-7,17 we show that a submonolayer concentration of nitrogen adsorbed on SiC, prior to graphene growth, causes a large band-gap to open in the subsequently grown, continuous graphene sheets. Using X-ray photoemission spectroscopy (XPS), scanning tunneling microscopy (STM), and angle resolved photoemission spectroscopy (ARPES), we show that a submonolayer concentration of bonded nitrogen at the graphene-SiC interface leads to a 0.7eV semiconducting form of graphene.The band-gap is not due to chemical functionalization since the concentrations used in these studies are expected to have little effect on graphene's band structure. 16,18 Instead, STM topographs and dI/dV images, showing that the graphene is buckled into folds with 1-2nm radii of curvature, suggests two possible origins for the gap: either a quasi-periodic strain 19 or electron localization in the 1-2 nm wide buckled ribbons. 20

Directional-dependent thickness and bending rigidity of phosphorene

“…Thus, non-uniform strains could be induced by placing PE on nanoscale patterns and on nanoparticles [21,22], or by pinning the 2D layer onto a substrate [23].…”

Pattern induced ordering of semiconducting graphene ribbons grown from nitrogen-seeded SiC

“…Instead, the nitrogen remains between the graphene and the SiC surface as schematically illustrated in Fig. 1(a) [5]. It is known from previous studies that the nitrogen bonding between the first graphene layer and the SiC causes the graphene to buckle as shown in Fig.…”

“…Furthermore, FETs built from monolayer C-face graphene have shown the highest operating frequencies of any graphene-based devices [4]. New experiments on C-face SiC have recently shown that graphene grown from a C-face surface seeded with nitrogen (N-Gr) produces a large band gap form of graphene [5]. The nitrogen induced gap is thought to be a result of a strain gradient caused by a graphene-nitrogen-SiC bond that forces the graphene to buckle [6,7].…”

“…An EDC through the Dirac point of the ribbons area [see Fig. 4(b)] shows a peak in the density of states (DOS) at 0.5 eV below E F signifying a band gap observed in nitrogen seeded graphene [5]. The DOS peak at the valence band maximum in Fig.…”

“…4(a) and (c), is due to both the buckled graphene and the spatial disorder in the film. The N-Gr buckling contribution to the diffuse Eðk y Þ spectrum is a result of the distribution of local surface normals [5] that cause electrons leaving different areas of the surface, with the same energy, to have different parallel momenta ðk x ; k y Þ. The result is that the analyzer simultaneously measures a wide set of slices through the Dirac cone, i.e., a set of constant k x conic sections through Eðk y ; k x Þ for a broad range of different k x values [18].…”