Bilayer Graphene Grown on 4H-SiC (0001) Step-Free Mesas

• Published in: Nano letters 2012-04, Vol.12 (4), p.1749-1756
• Main Authors: Nyakiti, L.O, Myers-Ward, R. L, Wheeler, V. D, Imhoff, E. A, Bezares, F.J, Chun, H, Caldwell, J. D, Friedman, A. L, Matis, B. R, Baldwin, J. W, Campbell, P. M, Culbertson, J. C, Eddy, C. R, Jernigan, G. G, Gaskill, D. K
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Electronics; Exact sciences and technology; Flats; Fullerenes and related materials; diamonds, graphite; Graphene; Materials science; Mesas; Nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals; Nanostructure; Physics; Silicon carbide; Specific materials; Strain; Structure of solids and liquids; crystallography; Transport; Variability
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl203353f

We demonstrate the first successful growth of large-area (200 × 200 μm2) bilayer, Bernal stacked, epitaxial graphene (EG) on atomically flat, 4H-SiC (0001) step-free mesas (SFMs) . The use of SFMs for the growth of graphene resulted in the complete elimination of surface step-bunching typically found after EG growth on conventional nominally on-axis SiC (0001) substrates. As a result heights of EG surface features are reduced by at least a factor of 50 from the heights found on conventional substrates. Evaluation of the EG across the SFM using the Raman 2D mode indicates Bernal stacking with low and uniform compressive lattice strain of only 0.05%. The uniformity of this strain is significantly improved, which is about 13-fold decrease of strain found for EG grown on conventional nominally on-axis substrates. The magnitude of the strain approaches values for stress-free exfoliated graphene flakes. Hall transport measurements on large area bilayer samples taken as a function of temperature from 4.3 to 300 K revealed an n-type carrier mobility that increased from 1170 to 1730 cm2 V–1 s–1, and a corresponding sheet carrier density that decreased from 5.0 × 1012 cm–2 to 3.26 × 1012 cm–2. The transport is believed to occur predominantly through the top EG layer with the bottom layer screening the top layer from the substrate. These results demonstrate that EG synthesized on large area, perfectly flat on-axis mesa surfaces can be used to produce Bernal-stacked bilayer EG having excellent uniformity and reduced strain and provides the perfect opportunity for significant advancement of epitaxial graphene electronics technology.