| AVS 56th International Symposium & Exhibition | |
| Graphene Topical Conference | Monday Sessions |
| Session GR+SS-MoA |
| Session: | Epitaxial Graphene on SiC |
| Presenter: | J.A. Robinson, The Pennsylvania State University Electro-Optics Center |
| Authors: | J.A. Robinson, The Pennsylvania State University Electro-Optics Center D. Snyder, The Pennsylvania State University Electro-Optics Center R. Cavalero, The Pennsylvania State University Electro-Optics Center K. Trumbull, The Pennsylvania State University Electro-Optics Center M. Wetherington, The Pennsylvania State University Electro-Optics Center E. Frantz, The Pennsylvania State University Electro-Optics Center M. LaBella, The Pennsylvania State University Electro-Optics Center Z. Hughes, The Pennsylvania State University Electro-Optics Center M.A. Fanton, The Pennsylvania State University Electro-Optics Center |
| Correspondent: | Click to Email |
Currently, the most promising route for large area graphene, suitable for standard device fabrication techniques, is the sublimation of silicon from silicon carbide (SiC) at elevated temperatures (>1200 °C). Prior to graphene synthesis, SiC substrates are generally hydrogen etched at elevated temperatures to remove residual polishing damage. However, this process can result in significant step bunching, and lead to large terrace step heights. We utilize various surface preparation conditions, Raman spectroscopy, and atomic force microscopy to investigate the nucleation and growth of epitaxial graphene on SiC(0001). The location of graphene was identified using a WITec confocal Raman microscope (CRM) with a 488 nm laser wavelength, diffraction limited lateral resolution of ~ 340 nm, and spectral resolution of 0.24 cm-1. The physical topography of the SiC substrate and graphene films were determined by atomic force microscopy using a Digital Instruments Nanoscope 3A.
We provide evidence that graphene not only nucleates at terrace step edges in the SiC surface, but also at surface defects such as residual surface damage from chemomechanical polishing, and screw dislocations. Prior to graphene synthesis samples were prepared in four manners: 1) in situ hydrogen (H2) etching; 2) ex situ potassium hydroxide (KOH) etching; 3) ex situ KOH and in situ H2 etching; 4) No etch. Potassium hydroxide selectively etches defect sites on the SiC surface, leaving behind etch pits which serve as macro-defects in the SiC surface. Our monolayer epitaxial graphene was synthesized via Si-sublimation from the Si-face of semi-insulating SiC at 1325°C, 1x10-6 Torr. These conditions preclude the formation of graphene on SiC(0001) except at terrace step edges and other topological defects, effectively decorating the nucleation sites for subsequent characterization.Samples with an in situ H2 etch exhibit growth of graphene nearly exclusively at terrace step edges, while KOH etched samples exhibit graphene synthesis primarily at the etch pits and terrace step edges in the SiC surface. Those samples that experience no pre-treatment exhibit the highest surface coverage of any surface preparation, indicating that graphene grown on SiC(0001) nucleates at atomic scale defects on the SiC surface. This work provides evidence that defects in the form of dislocations, terrace step edges, and etch pits act as low energy nucleation sites for the growth of epitaxial graphene on SiC(0001). Finally, this work suggests that the growth of uniform graphene on SiC(0001) will be heavily influenced by the SiC substrate quality.