Enabling graphene-based technologies: Toward wafer-scale production of epitaxial graphene
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Introduction Graphene is a single sheet of hexagonally bonded sp2 carbon atoms with two carbon atoms per unit cell. This arrangement gives rise to extraordinary physical properties, including ultrahigh intrinsic carrier (electron and hole) mobility, gate-tunable ambipolar carrier density, high current-density capacity, long-distance ballistic and spin transport, exceptionally low electronic noise, high thermal conductivity, and high elastic modulus—all of which were recently discussed and illustrated in an earlier MRS Bulletin article1 (also see the introductory article and the article by Ruan et al. in this issue). In addition, graphene devices can be fabricated using ostensibly the same techniques as currently employed by the silicon industry. These extraordinary attributes have attracted widespread attention for advanced device concepts including ultrasensitive molecular sensors;2 ultrafast, ultrawideband optical saturable absorbers,3 transparent conductors,4 and other photonic and optoelectronic applications;5 Klein-tunneling heterojunction devices;6 nanoelectromechanical systems;7 electrical signal frequency multipliers;8 electronic spin-transport devices;9 and high-frequency (on the order of terahertz) field-effect transistors (FETs).10
Yet, despite this immense technological potential, realizing the promise of pervasive device applications depends on the ability to controllably make large-area, uniformly thick, defect-free graphene layers on substrates compatible with current commercial processing technology. At this time, there are only two prospective approaches for making large-area graphene layers: (1) silicon sublimation from SiC substrates (described in this article) and (2) catalyzed growth on copper and other metal substrates (described in the article by Bartelt and McCarty in this issue). Formation of epitaxial graphene (EG) on SiC probably first occurred in the 1890s, when Edward Acheson developed a process for making SiC abrasives.11 His experiments on heated SiC indicated sublimation of silicon, leaving behind graphitic carbon12 on the surface; this process presumably, and without his knowledge at the time, started with the formation of graphene. The underpinnings of the mechanism of graphene formation advanced in 1975 when Van Bommel et al.13 reported differences in the rate of carbon formation between the two polar faces of SiC designated (0001) (the “Si face”) and (0001) (the
L.O. Nyakiti, Electronics Science and Technology Division, US Naval Research Laboratory; [email protected] V.D. Wheeler, Electronics Science and Technology Division, US Naval Research Laboratory; [email protected] N.Y. Garces, Electronics Science and Technology Division, US Naval Research Laboratory; [email protected] R.L. Myers-Ward, Electronics Science and Technology Division, US Naval Research Laboratory; [email protected] C.R. Eddy, Jr., Electronics Science and Technology Division, US Naval Research Laboratory; [email protected] D.K. Gaskill, Advanced SiC Epitaxi
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