Chemically Resolved Interface Structure of Epitaxial Graphene on SiC(0001)

Atomic-layer 2D crystals have unique properties that can be significantly modified through interaction with an underlying support. For epitaxial graphene on SiC(0001), the interface strongly influences the electronic properties of the overlaying graphene. We demonstrate a novel combination of x-ray scattering and spectroscopy for studying the complexities of such a buried interface structure. This approach employs x-ray standing wave-excited photoelectron spectroscopy in conjunction with x-ray reflectivity to produce a highly resolved chemically sensitive atomic profile for the terminal substrate bilayers, interface, and graphene layers along the SiC[0001] direction. DOI: 10.1103/PhysRevLett.111.215501 PACS numbers: 61.48.Gh, 61.05.cm, 68.49.Uv, 79.60.Ài Epitaxial graphene (EG) grown on the Si-terminated face of silicon carbide [SiC Early studies revealed that EG/SiC(0001) possesses a complex 6 p 3 Â 6 p 3R30 (6R3) reconstructed interfacial layer [10], referred to herein as the interfacial, or EG 0 , layer. This layer has significant influence on the growth, morphology, and electronic behavior of the overlaying graphene Because of the importance of the interfacial layer to the behavior of EG/SiC(0001), there have been numerous efforts to characterize its structure, including low-energy electron diffraction In this Letter we detail the structure of the interface by employing a suite of x-ray characterization techniques, including depth-sensitive XPS, x-ray standing waveenhanced XPS (XSW-XPS), and x-ray reflectivity (XRR). These tools, when employed collectively, provide the chemically specific structural information necessary to clarify previously unknown details of the EG/SiC(0001) interface. This approach ultimately enables the construction of a chemically resolved interfacial map with sub-Å resolution along the SiC[0001] direction. The XSW technique affords conventional photoelectron spectroscopy with high spatial resolution due to the influence of the XSW [here produced by the SiC(0006) Bragg reflection] on the photoabsorption process. A depiction of this phenomenon is shown i

Vertical conduction properties of few-layer epitaxial graphene / n-type 4H-SiC heterojunctions at cryogenic temperatures

Vertical diodes of epitaxial graphene on n 4H-SiC were investigated. The graphene Raman spectraexhibited a higher intensity in the G-line than the 2D-line, indicative of a few-layer graphene film.Rectifying properties improved at low temperatures as the reverse leakage decreased over six ordersof magnitude without freeze-out in either material. Carrier concentration of 10 16 cm 3in the SiCremained stable down to 15 K, while accumulation charge decreased and depletion width increasedin forward bias. The low barrier height of 0.08 eV and absence of recombination-induced emissionindicated majority carrier field emission as the dominant conduction mechanism

Investigation of the Epitaxial Graphene/p-SiC Heterojunction

There has been significant research in the study of in-plane charge-carrier transport in graphene in order to understand and exploit its unique electrical properties; however, the vertical graphene–semiconductor system also presents opportunities for unique devices. In this letter, we investigate the epitaxial graphene/p-type 4H-SiC system to better understand this vertical heterojunction. The I–V behavior does not demonstrate thermionic emission properties that are indicative of a Schottky barrier but rather demonstrates characteristics of a semiconductor heterojunction. This is confirmed by the fitting of the temperature-dependent I–V curves to classical heterojunction equations and the observation of band-edge electroluminescence in SiC

Graphene nanoribbon field-effect transistors on wafer-scale epitaxial graphene on SiC substrates

We report the realization of top-gated graphene nanoribbon field effect transistors (GNRFETs) of ∼10 nm width on large-area epitaxial graphene exhibiting the opening of a band gap of ∼0.14 eV. Contrary to prior observations of disordered transport and severe edge-roughness effects of graphene nanoribbons (GNRs), the experimental results presented here clearly show that the transport mechanism in carefully fabricated GNRFETs is conventional band-transport at room temperature and inter-band tunneling at low temperature. The entire space of temperature, size, and geometry dependent transport properties and electrostatics of the GNRFETs are explained by a conventional thermionic emission and tunneling current model. Our combined experimental and modeling work proves that carefully fabricated narrow GNRs behave as conventional semiconductors and remain potential candidates for electronic switching devices

Plasmon-Enhanced Terahertz Photodetection in Graphene

We report a large area terahertz detector utilizing a tunable plasmonic resonance in subwavelength graphene microribbons on SiC(0001) to increase the absorption efficiency. By tailoring the orientation of the graphene ribbons with respect to an array of subwavelength bimetallic electrodes, we achieve a condition in which the plasmonic mode can be efficiently excited by an incident wave polarized perpendicular to the electrode array, while the resulting photothermal voltage can be observed between the outermost electrodes

Plasmon-Enhanced Terahertz Photodetection in Graphene

We report a large area terahertz detector utilizing a tunable plasmonic resonance in subwavelength graphene microribbons on SiC(0001) to increase the absorption efficiency. By tailoring the orientation of the graphene ribbons with respect to an array of subwavelength bimetallic electrodes, we achieve a condition in which the plasmonic mode can be efficiently excited by an incident wave polarized perpendicular to the electrode array, while the resulting photothermal voltage can be observed between the outermost electrodes