2-D Electronic Materials: Epitaxial Growth Of Graphene On 6H-Silicon Carbide (0001)
Graphene holds great promise as a material for high-speed electronics, especially as Si technology approaches its performance limits. Growth of epitaxial graphene by thermal decomposition of SiC is considered to be one of the most promising production routes since it has the potential to produce homogenous, wafer-size films directly on a semi-insulating or semiconducting substrate. Furthermore, graphene's planar 2-D structure enables devices and circuit designs with standard top-down lithography and processing techniques. However, the growth mechanism of graphene on SiC is not very well understood and much work remains to be done to improve the morphology, domain size and epitaxial quality of the grown graphene in order to take advantage of the unique properties of the material. This research work was aimed at using a modified CVD chamber in the Cornell University Wide-Bandgap-Semiconductor Laboratory to optimize the growth of epitaxial graphene by controlled decomposition of 6H-SiC(0001) in an argon mediated gas flow at near atmospheric pressure. Grown films were characterized using Raman spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and electrical measurements. Uniform large-area monolayer and few-layer epitaxial graphene were successfully grown on SiC terraces of up to 8 [MICRO SIGN]m wide, and with Hall mobilities of up to 840 cm2/V.s. The as-grown graphene was found to be intrinsically electron doped with sheet carrier density in the range of 3 - 9 x 1012 cm-2. However, certain growth features that tended to disrupt growth by uniform step flow decomposition were observed. These included deep rounded pits at higher temperatures, shallow triangular pits, arrow-like incursions across terraces, finger growths, residual SiC islands on terraces, nucleation of graphene at multiple defect points on terraces, and extra graphene layers at step edges. Further research is required to determine the mechanisms of formation of these features and to determine how they can be eliminated or reduced. For the first time SiC grown epitaxial graphene films, transferred from the substrate by a special process, was imaged in plan-view by TEM. The TEM images, along with selected-area electron diffraction, showed that a bilayer film had the AB Bernal stacking. !
epitaxial graphene; 6H-silicon carbide
Spencer, Michael G.
Van Dover, Robert B.; Thompson, Michael Olgar
Ph.D. of Electrical Engineering
Doctor of Philosophy
dissertation or thesis