Temperature Dependence of Epitaxial Graphene Formation on SiC(0001)

Abstract

The formation of epitaxial graphene on SiC(0001) surfaces is studied using atomic force microscopy, Auger electron spectroscopy, electron diffraction, Raman spectroscopy, and electrical measurements. Starting from hydrogenannealed surfaces, graphene formation by vacuum annealing is observed to begin at about 1150°C, with the overall step-terrace arrangement of the surface being preserved but with significant roughness (pit formation) on the terraces. At higher temperatures near 1250°C, the step morphology changes, with the terraces becoming more compact. At 1350°C and above, the surface morphology changes into relatively large flat terraces separated by step bunches. Features believed to arise from grain boundaries in the graphene are resolved on the terraces, as are fainter features attributed to atoms at the buried graphene/SiC interface.

Formation of epitaxial graphene on SiC(0001) using vacuum or argon environments

“…Pits are formed during the initial stage, associated with the formation of the 6√3×6√3-R30° surface reconstruction. 12,13,14,15 This reconstruction persists as the graphene forms, located at the interface between the graphene and the SiC and thus acting as a template for the graphene formation. LEEM provides a direct measure of the thickness of a graphene film at each point on the surface, 16 revealing oscillations in the reflectivity of electrons which are dependent on the film thickness and beam energy.…”

Determination of the adhesion energy of graphene on SiC(0001) via measurement of pleat defects

“…1(b)) from which a thickness of 3 6 1 ML was estimated based on the height ratio of the C KLL and Si LMM peaks; the calibration curve used is produced from the determination of C:Si sensitivity factors. 24,25 This was supported by Raman spectroscopy measurements of the width of the 2D peak found at 2750 cm À1 . Raman measurements also indicated that the graphene is of a high quality due to the small size of the D peak observed at 1380 cm À1 (not shown).…”

The influence of the band structure of epitaxial graphene on SiC on the transistor characteristics

“…For our epitaxial graphene FETs with moderate mobilities compared to exfoliated graphene [2,22], we expect many mechanisms to coexist, among which the surface phonons and morphological disorder dominate, due to the use of the high-k dielectric [20] and the rough surface morphology (see AFM images in Refs. [9] and [23]), respectively. For the morphological disorder, it is reasonable to assume the mean free path v F τ as determined by surface roughness and average graphene domain size, thus independent of the carrier density.…”

“…Our epitaxial synthesis and thickness estimate of graphene on the Si-face have been described elsewhere [9]. The average thicknesses of both Si-face samples were estimated to be ~ 2 ML by Auger electron spectroscopy (AES) (this thickness does not include the C-rich "buffer layer" at the SiC/graphene interface [9]).…”

“…The average thicknesses of both Si-face samples were estimated to be ~ 2 ML by Auger electron spectroscopy (AES) (this thickness does not include the C-rich "buffer layer" at the SiC/graphene interface [9]). The synthesis on the C-face starts from a hydrogen etched substrate, and graphene formation is observed over the temperature range 1200-1400 ºC.…”