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In a hypothetical Grand Unified Theory, magnetic monopoles are a particle which would act as a charge carrier for the magnetic force. Evidence of magnetic monopoles has yet to be found and based off of their relatively high mass (4-10 TeV) will be difficult to find with current technology. The goal of my thesis is to mathematically model the magnetic monopole by finding numerical solutions to the equations of motion. In my analysis, I consider four cases: kinks, cosmic strings, global monopoles, and magnetic monopoles. I will also study electromagnetic gauge fields to prepare to include gauge fields in the magnetic monopole case. Numerical solutions are found for the cosmic string and global monopole cases. As expected, the energy is high at small distance r and drops off as r goes to infinity. Currently numerical solutions are being worked towards for electromagnetic gauge fields and the magnetic monopole case.
We present the results of experimentation with a superconducting nanowire that can be operated in two detection modes: i) as a kinetic inductance detector (KID) or ii) as a single photon detector (SPD). When operated as a KID mode in linear mode, the detectors are AC-biased with tones at their resonant frequencies of 45.85 and 91.81MHz. When operated as an SPD in Geiger mode, the resonators are DC biased through cryogenic bias tees and each photon produces a sharp voltage step followed by a ringdown signal at the resonant frequency of the detector. We show that a high AC bias in KID mode is inferior for photon counting experiments compared to operation in a DC-biased SPD mode due to the small fraction of time spent near the critical current with an AC bias. We find a photon count rate of $\Gamma_{KID} = 150~$photons/s/mA in a critically biased KID mode and a photon count rate of $\Gamma_{SPD} = 10^6~$photons/s/mA in SPD mode.
This dissertation additionally presents simulations of a DC-biased, frequency-multiplexed readout of SNSPD devices in Advanced Design System (ADS), LTspice, and Sonnet. A multiplexing factor of 100 is achievable with a total count rate of $>5$MHz. This readout could enable a 10000-pixel array for astronomy or quantum communications. Finally, we present a prototype array design based on lumped element components. An early implementation of the array is presented with 16 pixels in the frequency range of 74.9 to 161MHz. We find good agreement between simulation and experimental data in both the time domain and the frequency domain and present modifications for future versions of the array.
The effects of different growth conditions on the structural quality were thoroughly investigated. Lattice-matched condition was successfully achieved and material of exceptional quality was demonstrated.
After growth optimization had been achieved, structural defects could hardly be detected, so different characterization techniques, including etch-pit-density (EPD) measurements, cathodoluminescence (CL) imaging and X-ray topography (XRT), were explored, in attempting to gain better knowledge of the sparsely distributed defects. EPD revealed the distribution of dislocation-associated pits across the wafer. Unfortunately, the lack of contrast in images obtained by CL imaging and XRT indicated their inability to provide any quantitative information about defect density in these InAs/InAsSb T2SLs.
The nBn photodetectors based on mid-wave infrared (MWIR) and long-wave infrared (LWIR) InAs/InAsSb T2SLs were fabricated. The significant difference in Ga composition in the barrier layer coupled with different dark current behavior, suggested the possibility of different types of band alignment between the barrier layers and the absorbers. A positive charge density of 1.8 × 1017/cm3 in the barrier of MWIR nBn photodetector, as determined by electron holography, confirmed the presence of a potential well in its valence band, thus identifying type-II alignment. In contrast, the LWIR nBn photodetector was shown to have type-I alignment because no sign of positive charge was detected in its barrier.
Capacitance-voltage measurements were performed to investigate the temperature dependence of carrier densities in a metal-oxide-semiconductor (MOS) structure based on MWIR InAs/InAsSb T2SLs, and a nBn structure based on LWIR InAs/InAsSb T2SLs. No carrier freeze-out was observed in either sample, indicating very shallow donor levels. The decrease in carrier density when temperature increased was attributed to the increased density of holes that had been thermally excited from localized states near the oxide/semiconductor interface in the MOS sample. No deep-level traps were revealed in deep-level transient spectroscopy temperature scans.