Charge Carrier Transport and Strain in Graphene Grown on Nitrogen-Seeded Silicon Carbide
2017-10
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Charge Carrier Transport and Strain in Graphene Grown on Nitrogen-Seeded Silicon Carbide
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2017-10
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The interest in graphene as a possible basis for new, faster, smaller and more flexible electronics is tempered by its lack of a band-gap. In recent years, several methods by which a gap might be created have been proposed and explored. The work presented here is a part of that exploration. In this case, the specific gap-inducing mechanism under study is a method of engineered strain. Graphene can be grown on silicon carbide. By pre-treating the silicon carbide in a process that leaves small amounts of nitrogen on its surface, the subsequently grown graphene is made to wrinkle. By controlling the wrinkling, i.e. the strain in the graphene layer, it may be possible to induce a band-gap. Indeed, Angle-resolved photoemission spectroscopy and scanning tunneling spectroscopy results provide experimental support for this theory. At the same time, optical absorption measurements appear to contradict it. The primary focus of this dissertation is strain and transport measurements taken on devices fabricated from this type of graphene, with the expectation that these would aid in resolving the apparent contradiction in previous results.In the course of this work, a new tri-layer method of gate oxide deposition, using reactive electron beam deposition and plasma-assisted atomic layer deposition, was developed. Also, a method of enhanced Raman spectroscopy was developed for graphene-on-silicon-carbide devices. These methods were applied to a set of samples of graphene grown on nitrogen-seeded silicon carbide (NG) with the concentration of nitrogen varying between samples. In this dissertation, several transport characteristics are shown to exhibit a monotonic dependence upon the nitrogen concentration. These include changes in strain, broadening of the longitudinal resistivity peak, an offset between that peak and the zero-crossing of Hall conductivity, and a thermally activated n-doping mechanism, all measured with respect to an applied gate voltage. In addition, more complicated changes in temperature dependence and B-field dependence of the longitudinal resistivity are observed. These results, along with the surprising decrease in resistivity with the addition of nitrogen, are explained in the context of weak localization effects, increased transport by charge puddle-mediated tunneling, and edge states. While the presence of a band-gap could not be demonstrated conclusively in this, the first report of charge transport in this material, the results are in keeping with the presence of a band-gap short-circuited by edge states.
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University of Minnesota Ph.D. dissertation. October 2017. Major: Electrical/Computer Engineering. Advisors: Philip Cohen, P. Paul Ruden. 1 computer file (PDF); xiii, 179 pages.
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Torrey, Ethan R.. (2017). Charge Carrier Transport and Strain in Graphene Grown on Nitrogen-Seeded Silicon Carbide. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/201509.
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