| AVS 57th International Symposium & Exhibition | |
| Late Breaking Session | Wednesday Sessions |
| Session LB-WeA |
| Session: | Late Breaking Session Featuring Talks on Energy, Graphene and Atom-Probe Tomography |
| Presenter: | L.O. Nyakiti, U.S. Naval Research Laboratory |
| Authors: | L.O. Nyakiti, U.S. Naval Research Laboratory V.D. Wheeler, U.S. Naval Research Laboratory N. Garces, U.S. Naval Research Laboratory R.L. Myers-Ward, U.S. Naval Research Laboratory J.C. Culbertson, U.S. Naval Research Laboratory J.K. Hite, U.S. Naval Research Laboratory C.R. Eddy, Jr., U.S. Naval Research Laboratory F.J. Bezares, U.S. Naval Research Laboratory J.D. Caldwell, U.S. Naval Research Laboratory G.G. Jernigan, U.S. Naval Research Laboratory E.A. Imhoff, U.S. Naval Research Laboratory D.K. Gaskill, U.S. Naval Research Laboratory |
| Correspondent: | Click to Email |
Epitaxial graphene (EG) has exciting material properties that promise advancements in electronics, specifically in the fabrication of RF field-effect transistors. When EG is grown on the 4H- or 6H-SiC (0001), step-bunching occurs [1] with vertical morphology of 5 – 10 nm which poses a challenge to device development. Additionally, surface steps in graphene show a conductance difference between paths parallel and perpendicular to the step direction [2]. Hence to fabricate device structures, it is highly desirable to place devices on the relatively narrow (~2-4µm) terraces. In this work, we use large area, step-free 4H-SiC mesas (SFMs) to form EG and the results are found to mitigate the terrace (step bunching) related challenges present in traditional on-axis 4H-SiC (0001) wafer growth
Hexagonal and square SFMs with side dimensions ranging from 40 to 200 µm were formed by homoepitaxial growth of (0001) 4H-SiC layers [3] using a kinetically-controlled lateral step flow growth process at 15800C, resulting in atomically flat mesas devoid of surface defects. This was followed by EG growth in a 100 mbar Ar ambient at 1620°C for 1.5 or 2.5 hours. Nomarski microscopy was used in the identification of mesas having specular surfaces, or single stepped and defective surfaces. Micro-Raman spectroscopy and surface mapping using a laser excitation of 514.5 nm was employed to confirm the presence, thickness and strain variation of EG across the mesas. Veeco D3100 AFM (tapping mode) and LEO Supra 55 Scanning Electron Microscope was used to extract surface morphology variations across mesas.
Preliminary results show that 1.5 and 2.5 hours of EG growth were more than sufficient for complete uniform monolayer and bilayer graphene coverage on the mesas, respectively. The surface of the EG on SFMs had atomic steps ≤ 0.6 nm, a reduction in step-height by a factor of 30 from typically grown step-bunched graphene on 4H-SiC (0001) substrates. Raman 2D peak position maps for monolayer and bilayer regions show relatively low strain (~2700cm-1) coverage with the former approaching values close to exfoliated graphene (~2696cm-1). Thus, the use of large area SFMs for EG has resulted in novel characteristics that holds great promise towards controlling layer thickness homogeneity without step bunching and having minimal strain.
References
[1] Tedesco, J. L.; et al ECS Trans. 2009, 19, 137-150.
[2] Yakes, M. Y.; et al Nano lett. 2010, 10, 1559-1562.
[3] Neudeck, P. G.; et al MRS symp. Proc. 911, 2006