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Toward nanowire devices and systems : heterostructure design and dielectrophoretic integration


Successes in the growth and fabrication of semiconductor nanowires, have led to new opportunities in device design for a wide variety of applications. Nanowires provide unique opportunities in device engineering in that their properties can be manipulated and tailored at the time of their creation to meet specific functional applications. Such nanowire devices can then be harvested to serve as building blocks for larger integrated systems. This is typically referred to as the "bottom-up" approach and adds a degree of flexibility not available in planner device fabrication. In this dissertation we will exam on a few specific aspects of semiconductor device and system engineering. Specifically we examine the geometric limits for coherence in radial nanowire heterostructures as well as the use of electric fields to align and place nanowires. Novel nanowire device designs often require, or can benefit from, the use of heterostructures in their design. In determining the feasibility of these designs it is necessary to consider the strain that arises in heterostructures due to the lattice mismatch between materials. Such strain not only affects the electronic and optical properties of the device, but also determines the device dimensions at which coherence is lost and dislocations form, which will significantly alter or degrade device performance. In the second chapter of this dissertation we present a methodology to predict critical dimensions for coherently strained coaxial nanowire heterostructures based on a well-known formalism used to determine the critical thickness in planar epitaxial growth. It is anticipated that this model will serve as a guide to determine the feasibility of specific coherently strained nanowire heterostructure device designs. While many individual nanowire devices and structures have been demonstrated, there are very few examples of large (or moderately sized) nanowire systems. Manipulating and placing nanowires in a useful fashion continues to be a considerable challenge. In the final chapter of this dissertation nanowire placement using Dielectrophoresis (DEP) is explored. DEP refers to the use of electric fields to manipulate neutrally charged particles in solution and can be used to attract nanowires (suspended in solution) onto predefined electrodes. DEP offers the ability to assemble a wide variety of nanowires and is not limited by the way in which a nanowire is fabricated. Experimental results are presented and discussed demonstrating the feasibility of DEP as means to construct nanowire systems

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