Ultrathin epitaxial graphite was grown on single-crystal silicon carbide by vacuum graphitization. The material can be patterned using standard nanolithography methods. The transport properties, which are closely related to those of carbon nanotubes, are dominated by the single epitaxial graphene layer at the silicon carbide interface and reveal the Dirac nature of the charge carriers. Patterned structures show quantum confinement of electrons and phase coherence lengths beyond 1 micrometer at 4 kelvin, with mobilities exceeding 2.5 square meters per volt-second. All-graphene electronically coherent devices and device architectures are envisaged.

https://science.sciencemag.org/content/sci/312/5777/1191.full.pdf

Electronic Confinement and Coherence in Patterned Epitaxial Graphene

http://absimage.aps.org/image/MAR07/MWS_MAR07-2006-006269.pdf

We have produced ultrathin epitaxial graphite films which show remarkable 2D electron gas (2DEG) behavior. The films, composed of typically three graphene sheets, were grown by thermal decomposition on the (0001) surface of 6H−SiC, and characterized by surface science techniques. The low-temperature conductance spans a range of localization regimes according to the structural state (square resistance 1.5 kΩ to 225 kΩ at 4 K, with positive magnetoconductance). Low-resistance samples show characteristics of weak localization in two dimensions, from which we estimate elastic and inelastic mean free paths. At low field, the Hall resistance is linear up to 4.5 T, which is well-explained by n-type carriers of density 1012 cm-2 per graphene sheet. The most highly ordered sample exhibits Shubnikov−de Haas oscillations that correspond to nonlinearities observed in the Hall resistance, indicating a potential new quantum Hall system. We show that the high-mobility films can be patterned via conventional lithographic...

Ultrathin epitaxial graphite: 2D electron gas properties and a route toward graphene-based nanoelectronics.

Graphene: Synthesis and applications

The electronic properties of epitaxial graphene grown on SiC have shown its potential as a viable candidate for post-CMOS electronics. However, progress in this field requires a detailed understanding of both the structure and growth of epitaxial graphene. To that end, this review will focus on the current state of epitaxial graphene research as it relates to the structure of graphene grown on SiC. We pay particular attention to the similarity and differences between graphene growth on the two polar faces, (0001) and , of hexagonal SiC. Growth techniques, subsequent morphology and the structure of the graphene/SiC interface and graphene stacking order are reviewed and discussed. Where possible the relationship between film morphology and electronic properties will also be reviewed.

https://iopscience.iop.org/article/10.1088/0953-8984/20/32/323202/pdf

The growth and morphology of epitaxial multilayer graphene

Magnesium incorporation during the molecular-beam epitaxy growth of wurtzite GaN is found to invert the Ga-polar (0001) face to the N-polar face. The polarity is identified based on the two different sets of reconstructions seen on the film prior to and after about 1 monolayer Mg exposure. The inversion boundary is seen to lie on the (0001) plane from transmission electron microscopy images, and a structural model is presented for the inversion. On the Ga-polar face, Mg is also seen to stabilize growth in the N-rich regime.

/pdf/inversion-of-wurtzite-gan-0001-by-exposure-to-magnesium-2w5kr04zeu.pdf

Inversion of wurtzite GaN(0001) by exposure to magnesium

Hydrogen etching of 6H- and 4H-SiC(0001) surfaces is studied. The aspolished substrates contain a large number of scratches arising from the polishing process which are eliminated by hydrogen etching. Etching is carried out in a flow of hydrogen gas at atmospheric pressure and temperatures around 1600-1700 C attained on a tantalum strip heater. Post-etching atomic force microscopy (AFM) images show periodic arrays of atomically flat terraces that are a few thousand A wide. These terraces are separated by steps 15 A high in the directions. Often, the surface is seen to be faceted with steps on neighbouring facets forming 60 angles and offset in the c-direction by half a unit cell. Images of incompletely etched surfaces show early stages of etching where one can see remnants of surface damage in the form of arrays of hexagonal pits. On the larger scale, the surface has a hill-and-valley type morphology. The observed features are interpreted in a model based on the symmetry of the SiC unit cell and crystal miscut.

/pdf/preparation-of-atomically-flat-surfaces-on-silicon-carbide-p8ugtcvw7p.pdf

Preparation of atomically flat surfaces on silicon carbide using hydrogen etching

Surface reconstructions during homoepitaxial growth of GaN (0001) are studied using reflection high-energy electron diffraction and scanning tunneling microscopy. In agreement with previous workers, a distinct transition from rough to smooth morphology is seen as a function of Ga to N ratio during growth. However, in contrast to some prior reports, no evidence for a 2×2 reconstruction during GaN growth is observed. Observations have been made using four different nitrogen plasma sources, with similar results in each case. A 2×2 structure of the surface can be obtained, but only during nitridation of the surface in the absence of a Ga flux.

/pdf/surface-reconstruction-during-molecular-beam-epitaxial-2wsv7sfn78.pdf

Surface Reconstruction during Molecular Beam Epitaxial Growth of GaN (0001)

We report studies of the surface reconstructions for both the Ga-face and the N-face of wurtzite GaN films grown using molecular beam epitaxy. N-face reconstructions are primarily adatom-on-adlayer structures which can be formed by room temperature submonolayer Ga deposition. These structures undergo reversible order–disorder phase transitions to 1×1 in the temperature range of 200–300 °C. Ga-face reconstructions, on the other hand, require annealing to high temperatures (600–700 °C) in order to form, and in most cases they are stable at those temperatures. The film polarity is found to be determined by the initial nucleation stage of the film growth.

/pdf/wurtzite-gan-surface-structures-studied-by-scanning-1v6ozgmb2f.pdf

Wurtzite GaN surface structures studied by scanning tunneling microscopy and reflection high energy electron diffraction

https://www.cmu.edu/physics/stm/publ/22/arsen1.pdf

V. Ramachandran

Papers

Inversion of wurtzite GaN(0001) by exposure to magnesium

Preparation of atomically flat surfaces on silicon carbide using hydrogen etching

Surface Reconstruction during Molecular Beam Epitaxial Growth of GaN (0001)

Wurtzite GaN surface structures studied by scanning tunneling microscopy and reflection high energy electron diffraction

Structure of clean and arsenic-covered GaN(0 0 0 1) surfaces