WELDING OF SEMICONDUCTOR NANOWIRES: INITIAL JOINING METHODS, OHMIC JUNCTION FORMATION AND SCALE UP

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  • March 22, 2019
Creator
  • Celano, Tom
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • Single nanowires (NW) have been utilized in a variety of technological applications including optics, energy harvesting, biological/mechanical sensing, electrode scaffolds and other electronic devices. Metallic NW networks have even begun to replace traditional transparent conducting oxides (TCO) in touchscreen electronics, due to the simple solution phase growth and welding processes required to form the network. Unfortunately, semiconductor nanowires exhibit unique challenges during scale-up. One large benefit to semiconductor NWs when compared to metallic analogs, is semiconductor NWs can have functionality encoded via dopant incorporation in-situ and post growth. Unfortunately, large-scale processing of bottom-up grown semiconductor NWs is difficult - often a multi-stage, time consuming process. To overcome this impediment we have developed a process that welds NWs at each point of contact, generating a dense interconnected network of NWs separated by ohmic and highly crystalline junctions. Using the Vapor Liquid Solid (VLS) growth process, we collapsed and annealed NWs at temperatures 400 to 600 °C below the bulk melting point of Si and Ge, resulting in a large area interconnected network with variable density, NW diameter and optical response. Junctions are polycrystalline, devoid of native oxide and exhibit low junction resistance. Capillarity induced surface diffusion was used to simulate the welding process across different geometries. We determined that junctions exhibited low resistance and networks exhibited relatively uniform electrical connectivity across large regions. Films were able to be fully removed from growth substrates and contained within PDMS stamps. The resulting PDMS embedded NW networks were mechanically robust and showed only a minor increase in resistance when compared with an analogous network on a growth substrate. Welded semiconductor NW networks show promise for a variety of technological applications and we believe the weld process can be generalized for different nanomaterials.
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Advisor
  • Cahoon, James
  • Kanai, Yosuke
  • You, Wei
  • Warren, Scott
  • Moran, Andrew
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2018
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