Synthetically Controlling Doping and Nanoscale Morphology in Vapor-Liquid-Solid Grown Silicon Nanowires to Encode Functionality Public Deposited

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  • March 21, 2019
  • Christesen, Joseph
    • Affiliation: College of Arts and Sciences, Department of Chemistry
  • Control of morphology and composition on nanometer length scales is a necessary tool for tuning the optical and electrical properties of semiconductor devices. Currently, this is achieved through “top-down” lithographic fabrication techniques, which are prohibitive due to high costs, increased complexity, and/or low throughput. Therefore, a new strategy is needed in order to create low cost and scalable method for fabricating nanomaterials for future semiconductor applications. Semiconductor nanowires (NWs) synthesized through the vapor-liquid-solid (VLS) mechanism are an ideal nanomaterial, as they enable rational synthetic control over composition, morphology, and corresponding properties of the NW from the atomic to microscopic scale. First, we report a bottom-up method to break the conventional “wire” symmetry and synthetically encode a high-resolution array of arbitrary shapes along the NW growth axis. Rapid modulation of phosphorus doping combined with selective wet-chemical etching enables morphological features as small as 10 nm to be patterned over wires more than 50 μm in length. We then investigate the abruptness of these heterojunctions, which is important for a range of technologies. The abruptness of the heterojunction is mediated by the liquid catalyst, which can act as a reservoir of material and impose a lower limit on the junction width. We demonstrate that this “reservoir effect” is not a fundamental limitation and can be suppressed by selection of specific VLS reaction conditions. Using this precise control of the morphology of the Si NW, we were able synthesis a variety of devices with applications in optics, electronics, and computation. Finally, we investigate the effect of device geometry and compositional control over the photovoltaic performance of axial and radial Si NW p–n junctions through finite-element simulations. We compare simulated current–voltage data to experimental measurements, permitting detailed analysis of NW performance, limitations, and prospect as a technology for solar energy conversion.
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  • In Copyright
  • Moran, Andrew
  • Cahoon, James
  • Papanikolas, John
  • Lopez, Rene
  • Atkin, Joanna
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2016

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