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**UNC-CH Physics and Astronomy Honors Thesis Defense**

Jeremy Low

**“Asymmetrically etched p-type silicon nanowires as geometric diodes”**

Geometric diodes operate, not due to potential barriers, but due to the shape of the device. Nanowire geometric diodes have unique properties which allow them to function as long wavelength energy harvesters and ultra-high speed signal processors. Geometric diodes operate through symmetry breaking on a scale comparable to the mean-free-path length of charge carriers, generating an asymmetry which we define as the current at some positive bias V_{0} divided by the current at the reverse bias –V_{0}. Silicon nanowires, encoded with sawtooth geometries, exhibit diode-like behavior. Current at an applied voltage is directionally asymmetric due to the geometric diode effect. Sawtooth geometries are defined by three parameters, sawtooth length, inner diameter, and outer diameter, and a parameter, taper length that isn’t directly tunable, and all impact the overall resistance, I-V characteristics and frequency dependence. These parameters are controlled through the growth, dopant encoding via a vapor-liquid-solid mechanism, and subsequent etching of the nanowire. With tuning of these parameters a device with desired diode-like properties and frequency response can be developed. To maximize the operating frequency of the diodes we develop devices with a minimized resistance, therefore minimized RC time constant. In this project we characterize these novel devices, determining the dependence of their electronic properties on geometric parameters, mean-free-path, and surface treatments. Better understanding these parameters will facilitate the optimization of the devices, as well as manufacturing processes, for applications in ultra-fast signal processing, and for novel long-wavelength energy harvesting.