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Spectroscopic Mapping Ellipsometry of Graphene Grown on 3C SiC Alexander Boosalis1, Tino Hofmann1, Vanya Darakchieva2, RositzaYakimova2, Tom Tiwald3, and Mathias Schubert1 1

Department of Electrical Engineering, University of Nebraska–Lincoln, Lincoln, Nebraska, U.S.A. 2 Department of Physics, Linköping University, Linköping Sweden. 3 J.A. Woollam Co., Lincoln, Nebraska, U.S.A. ABSTRACT Spectroscopic mapping ellipsometry measurements in the visible spectrum (1.25 to 5.35 eV) are performed to determine the lateral variations of epitaxial graphene properties as grown on 3C SiC. Data taken in the visible spectrum is sensitive to both the Drude absorption of free charge carriers and the characteristic exciton enhanced van Hove singularity at 5 eV. Subsequent analysis with simple oscillator models allows the determination of physical parameters such as free charge carrier scattering time and local graphene thickness with a lateral resolution of 50 microns. INTRODUCTION Recent research has shown graphene to exhibit superior electronic properties to silicon leading to a demand for epitaxial graphene production [1, 2]. Successful deposition of epitaxial graphene onto large scale substrates, perhaps by thermal sublimation of silicon carbide, may offer realization of a new generation of electronic devices. Recently, fabrication of field-effect transistor devices on epitaxial graphene with cut-off frequencies in excess of fifty gigahertz was achieved [3]. In order to harness graphene for commercial production, further development of epitaxial growth processes must continue and a better understanding of the electronic and structural relationships in epitaxial graphene must be reached [4, 5]. In order to better understand the influences of substrate morphology and surface preparation on graphene growth and resulting electronic properties we must investigate the laterally varying dielectric function of epitaxial graphene films. The dielectric function spectra are unique fingerprints of the electronic properties of semiconductor materials, and are suitable for characterization of electronic band structure parameters. Likewise, these functions can be used for monitoring structure-related properties such as strain, as well as for quality control during production. Theoretical calculations predict a van Hove singularity within the 2-dimensional Brilloiun zone along the 6-fold degenerate directions between symmetry points K and K' [6]. This singularity can be associated with the characteristic critical-point feature observed in dielectric function spectra of exfoliated graphene [7, 8], and graphene grown by chemical vapor deposition for photon energies around 5~eV [9]. It is of interest to monitor these critical-point features as a function of position, which may reflect differences in strain and dopant and defect incorporation of the epitaxial graphene layers.

The physical parameter maps reported here are obtained from spectroscopic ellipsometry measurements and subsequent model dielectric function analysis. We employ traditional