Wu, Yudong (2011)
Ph.D. thesis, University of Birmingham.
Since the publication of research in the mid-1980s describing the formation of freeform graphene there has been an enormous growth in interest in the material. Graphene is of interest to the semiconductor industry because of the high electron mobility exhibited by the material and, as it is planar, it is compatible with silicon technology. When patterned into nanoribbons graphene can be made into regions that are semiconducting or conducting and even into entire circuits. Graphene nanoribbons can also be used to form the channel of a MOSFET. This thesis describes numerical simulations undertaken on devices formed from graphene. The energy band structure of graphene and graphene nanoribbons is obtained using nearest-neighbour and third nearest-neighbour interactions within a tight binding model. A comparison of the current-voltage characteristics of MOS structures formed on graphene nanoribbons and carbon nanotubes suggests that the nanoribbon devices may be better for switching applications. Conductivities of graphene nanoribbons and junctions formed from them were obtained using a nonequilibrium Green’s function formulation. The effects of defects and strain on these systems were also studied using this technique. Advancements were made when the self-energies used within the nonequilibrium Green’s function were obtained from an iterative scheme including third nearestneighbour interactions. An important result of this work is that accurate simulations of graphene based devices should include third nearest-neighbour interactions within the tight binding model of the energy band structure.
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