We report on the structural and electronic properties of graphene grown on SiC by high-temperature sublimation. We have studied thickness uniformity of graphene grown on 4H-SiC(0001), 6H-SiC(0001), and 3C-SiC(111) substrates and investigated in detail graphene surface morphology and electronic properties. Differences in the thickness uniformity of the graphene layers on different SiC polytypes is related mainly to the minimization of the terrace surface energy during the step bunching process. It is also shown that a lower substrate surface roughness results in more uniform step bunching and consequently better quality of the grown graphene. We have compared the three SiC polytypes with a clear conclusion in favor of 3C-SiC. Localized lateral variations in the Fermi energy of graphene are mapped by scanning Kelvin probe microscopy. It is found that the overall single-layer graphene coverage depends strongly on the surface terrace width, where a more homogeneous coverage is favored by wider terraces. It is observed that the step distance is a dominating, factor in determining the unintentional doping of graphene from the SiC substrate. Microfocal spectroscopic ellipsometry mapping of the electronic properties and thickness of epitaxial graphene on 3C-SiC (111) is also reported. Growth of one monolayer graphene is demonstrated on both Si-and C-polarity of the 3C-SiC substrates and it is shown that large area homogeneous single monolayer graphene can be achieved on the Si-face substrates. Correlations between the number of graphene monolayers on one hand and the main transition associated with an exciton enhanced van Hove singularity at ∼4.5 eV and the free-charge carrier scattering time, on the other are established. It is shown that the interface structure on the Si-and C-polarity of the 3C-SiC(111) differs and has a determining role for the thickness and electronic properties homogeneity of the epitaxial graphene.

Unraveling the doping-related charge carrier scattering mechanisms in two-dimensional materials such as graphene is vital for limiting parasitic electrical conductivity losses in future electronic applications. While electric field doping is well understood, assessment of mobility and density as a function of chemical doping remained a challenge thus far. In this work, we investigate the effects of cyclically exposing epitaxial graphene to controlled inert gases and ambient humidity conditions, while measuring the Lorentz force-induced birefringence in graphene at Terahertz frequencies in magnetic fields. This technique, previously identified as the optical analogue of the electrical Hall effect, permits here measurement of charge carrier type, density, and mobility in epitaxial graphene on silicon-face silicon carbide. We observe a distinct, nearly linear relationship between mobility and electron charge density, similar to field-effect induced changes measured in electrical Hall bar devices previously. The observed doping process is completely reversible and independent of the type of inert gas exposure.

In this work, we report a muti-scale investigation using several nano-, micro and macro-scale techniques of few layer graphene (FLG) sample consisting of large monolayer (ML) and bilayer (BL) areas grown on C-face 4H-SiC (000-1) by high-temperature sublimation. Single 1×1 diffraction patterns are observed by micro-low-energy electron diffraction for ML, BL and trilayer graphene with no indication of out-of-plane rotational disorder. A SiO x layer is identified between graphene and SiC by X-ray photoelectron emission spectroscopy and reflectance measurements. The chemical composition of the interface layer changes towards SiO 2 and its thickness increases with aging in normal ambient conditions. The formation mechanism of the inter- *

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We show experimentally that few layer graphene (FLG) grown on the carbon terminated surface (C-face) of 3C-SiC(111) is composed of decoupled graphene sheets. Landau level spectroscopy on FLG graphene is performed using the infrared optical Hall effect. We find that Landau level transitions in the FLG exhibit polarization preserving selection rules and the transition energies obey a square-root dependence on the magnetic field strength. These results show that FLG on C-face 3C-SiC(111) behave effectively as a single layer graphene with linearly dispersing bands (Dirac cones) at the graphene K point. We estimate from the Landau level spectroscopy an upper limit of the Fermi energy of about 60 meV in the FLG, which corresponds to a carrier density below 2.5 × 1011 cm−2. Low-energy electron diffraction μ-LEED) reveals the presence of azimuthally rotated graphene domains with a typical size of ≤200 nm. μ-LEED mapping suggests that the azimuth rotation occurs between adjacent domains within the same sheet rather than vertically in the stack.

We study the effect of nitrogen on the GaAs0.9−xNxSb0.1 (x=0.00, 0.65%, 1.06%, 1.45%, and 1.90%) alloy dielectric function by spectroscopic ellipsometry in the energy range from 0.73 to 4.75 eV. The compositional dependences of the critical points energies for the GaAs0.9−xNxSb0.1 are obtained. In addition to the GaAs intrinsic transitions E1, E1+Δ1, and E0′, the nitrogen-induced Γ-point optical transitions E0 and E+, together with a third transition E#, are identified. We find that with increasing the N content, the E0 transition shifts to lower energies while the E+ and E# transitions shift to higher energies. We suggest that the origin of the E0, E+, and E# transitions may be explained by the double band anticrossing (BAC) model, consisting of a conduction BAC model and a valence BAC model.

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Understanding and controlling growth of graphene on the carbon face (C-face) of SiC presents a significant challenge. In this work, we study the structural, vibrational, and dielectric function properties of graphene grown on the C-face of 4H-SiC by high-temperature sublimation in an argon atmosphere. The effect of growth temperature on the graphene number of layers and crystallite size is investigated and discussed in relation to graphene coverage and thickness homogeneity. An amorphous carbon layer at the interface between SiC and the graphene is identified, and its evolution with growth temperature is established. Atomic force microscopy, micro-Raman scattering spectroscopy, spectroscopic ellipsometry, and high-resolution cross-sectional transmission electron microscopy are combined to determine and correlate thickness, stacking order, dielectric function, and interface properties of graphene. The role of surface defects and growth temperature on the graphene growth mechanism and stacking is discussed, and a conclusion about the critical factors to achieve decoupled graphene layers is drawn