Modulating Optical and Electronic Properties in Silicon Nanowire Superlattices Public Deposited

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  • March 21, 2019
  • Hill, David
    • Affiliation: College of Arts and Sciences, Department of Chemistry
  • Here, we develop new techniques for implementing silicon nanowires (NWs) in complex photonic and electronic applications. First, we present waveguide scattering microscopy (WSM) as an alternative technique to dark-field microscopy (DFM) to image and analyze photonic nanostructures. WSM uses a white-light source coupled to a dielectric slab waveguide to generate an evanescent field that illuminates objects on the waveguide surface. We demonstrate high-contrast dark-field imaging of nanophotonic and plasmonic structures such as Si nanowires, Au nanorods, and Ag nanoholes. Scattering spectra collected in the WSM configuration show excellent signal-to-noise with minimal background signal compared to conventional DFM. In addition, the polarization of the incident field is controlled by the direction of the propagating wave, providing a straightforward route to excite specific optical modes in anisotropic nanostructures. We also overcome several difficulties of VLS NW growth, such as nonselective deposition, kinking, and compositional gradients, and report the synthesis of uniform, linear, and degenerately doped Si NW superlattices. The synthesis is enabled by in situ chlorination of the NW surface with hydrochloric acid. We find the boron doping level to far exceed the solid solubility limit, resulting from crystallization kinetics. Because the boron and phosphorus doping levels are degenerate, both segments inhibit the etching of Si in basic solutions. Moreover, we find that the dopant transitions are abrupt, facilitating morphological control with a spatial resolution of ~10 nm. We delineate how the photovoltaic performance of NWs with axial p-i-n junctions is dictated not simply by the surface but also by the complex interplay of diode geometry - i.e. radius (R) and intrinsic length (Li) - with the surface recombination velocity (S). Using a combination of finite-element simulations, analytical theory, and single-NW measurements, we evaluate the dependence of the dark saturation current (Io), internal quantum efficiency (IQE), short-circuit current (Isc), and open-circuit voltage (Voc) on both geometric and recombination parameters, highlighting various trade offs in the performance metrics. The results presented herein enable the growth of complex, degenerately doped p-n junction nanostructures and provide guidance for the rational design of photodiode and photovoltaic devices that can be explored for advanced NW architectures.
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  • In Copyright
  • Liebfarth, Frank
  • Cahoon, James
  • Dempsey, Jillian
  • Warren, Scott
  • Atkin, Joanna
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2018

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