Multi-Physics Analysis of Graphene Nanoribbon (GNR) for Application in Power Electronics
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Ever since the first experimentally discovered, graphene is quickly rising to be one of the most attractive material systems for potential applications due to its unique properties. It is the thinnest object ever obtained; very elastic and the world's strongest material; its charge carriers are massless Dirac fermions; it is extremely electrically and thermally conductive; etc. The planar form of graphene suggesting that some variant of the well-developed top-down complementary metal oxide semiconductor (CMOS) compatible process flow may be developed for fabrication of graphene-based devices. This promises a substantial advantage over carbon nanotubes (CNTs), which are difficult to integrate into electronic devices and are difficult to produce in consistent sizes and electronic properties. In most applications of graphene, graphene nanoribbon (GNR) is the most common form. There are various reasons for using graphene in GNR form, e.g. introducing energy band gap by width restriction, using GNR as interconnects for electronics, using it as elements of more complex mechanical structures, and appealing fabrication method of unzipping carbon nanotubes (CNT), and so on. In all applications, mechanical properties of GNRs are always one of the fundamental issues to consider. Due to difficulties in the fabrication and manipulation of GNRs, however, few information is available on this topic. In this thesis, extensive parametric studies have been done for effects of size, aspect ratio, chirality, and hydrogen passivation. In contrast to CNTs, the absence of translational symmetry (or periodical boundary condition) in the restricted direction of ZGNR removes the selection rule of sub-band number conservation and introduces the so called 'transverse momentum conservation uncertainty'. In this work, we propose and demonstrate the selection rule of parity conservation based on the mirror symmetry of ZGNR with even dimers. Using full-band electron and phonon dispersion relations, the temperature dependence of Joule heating in Zigzag Graphene Nanoribbons under high electrical field is investigated. The Joule heating at different temperatures always increases linearly with time, therefore the Joule heating power is a constant. Because more scattering mechanisms are available for electrons in Zigzag Graphene Nanoribbon, it has higher Joule heating power than Single-Walled Carbon Nanotube. At temperatures of 300K, 600K, and 900K, the Joule heating power of Zigzag Graphene Nanoribbon has the ratio 1:6.7:12.6. This is explained approximately by the relationship between energy transferring rates and average phonon energy in phonon modes.