Call number: LD2668 .T4 1963 W87 / Master of Science

A one-dimensional analytical model of dark current has been developed to facilitate the investigation and analysis of dark current from gate-controlled photovoltaic InSb arrays. The applied gate voltage is an essential parameter in the model. The expressions relating this parameter to surface potential are derived separately for the cases of accumulation and depletion at the surface of n-type InSb material under the gate. In addition, the measured dark current is compared with that from the analytical model, and the discrepancy is discussed in terms of the intrinsic carrier concentration, surface recombination velocity, and geometry of the array. The components of dark current are mainly associated with surface state generation-recombination, field induced tunneling, and the depletion region from the bulk and surface. The experimental results are obtained at temperatures between 30K and 40K.

Thesis (Ph. D.)--University of Wisconsin, 1966. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

Highly sensitive magneto-optical techniques have been used to investigate weak linear and nonlinear optical absorption mechanisms in p- and n-type InSb. As a result, new absorption processes involving both impurities and free carriers have been identified and studied in detail. For p-InSb, magneto-optical spectra has been obtained over a wide range of temperatures and photon energies. The spectra obtained at higher sample temperatures are seen to result from combined-resonance transitions of free holes between heavy-and light-hole Landau levels, while bound-hole transitions between ground heavy-hole-like and excited light-hole-like acceptor states are observed at lower temperatures. Analysis of the combined-resonance data along with extensive intra-conduction band and two-photon interband data using a modified Pidgeon and Brown 8X8 energy band model has allowed the determination of a single set of band parameters for InSb that quantitatively describes these different sets of data. In addition, a ground state binding energy of 8.1 meV for Cd acceptors and 42.5 meV for Au acceptors has been extracted from the analysis of the bound-hole spectra. For n-lnSb, photo-Hall techniques have been developed and used to study both resonant impurity and two-photon magneto-absorption (TPMA) processes in detail. As a result, LO-phonon-assisted impurity cyclotron resonance harmonic (LOICRH) transitions from the shallow Te donor level have been observed for the first time. In addition, transitions from deep levels are also observed in the photo-Hall signal obtained at sample temperatures greater than 20K. Both time-resolved and intensity-dependent measurements on impurity and TPMA processes are reported and the results compared directly with the predictions of rate equations describing the photoexcited carrier dynamics. These investigations have yielded important information about the optical properties of n-InSb; e.g. impurity and two-photon absorption coefficients, photo-excited carrier lifetimes, and recombination rates.

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This thesis is a study of the structural, electrical and magnetic properties of indium antimonide (InSb) nanowires (NWs), that were synthesized by a template-assisted ordered growth technique via electrochemical deposition. InSb was chosen for this study because of its intrinsic properties that make it a material of choice for applications in high channel mobility, infrared (IR) sensing, thermoelectrics, and magnetoresistive sensing martials. This work has four main components: (i) Growth in commercially available anodic aluminum oxide (AAO) template, where hole-dominated conduction was observed, following NW growth in a low pH electrolyte. The challenge in using these AAO templates was in covering the back surface of the pores with a metal film. Uncovered pores resulted in electrolyte leakage and non-reproducible results. (ii) Growth in flexible polycarbonate membranes, where the flexibility of the membranes resulted in polycrystalline or high defect density NW growth. (iii) Fabrication of an AAO template, where the barrier layer thinning technique was found to be efficient in removal of the think aluminum oxide barrier that exists at the interface between the template and the aluminum metal. This allows for direct growth of NWs into the template pores without the need for metal evaporation. (iv) Fabrication of a heterostructure comprising of an InSb layer sandwiched between two ferromagnetic contacts. Preliminary results show evidence of inverse spin-valve effect at the low temperature of 4K.

Thesis advisor: Michael J. Graf / Quantum spin liquids (QSL)’s have been one of the most hotly researched areas ofcondensed matter physics for the past decade. Yet, science has yet to unconditionally identify any one system as harboring a QSL state. This is because QSL’s are largely defined as systems whose electronic spins do not undergo a thermodynamic transition as T→0. Quantum spin liquids remain fully paramagnetic, including dynamical spin fluctuations, at T=0. As a result, distinguishing a QSL system from a conventionally disordered system remains an outstanding challenge. If a system spin freezes or magnetically orders, it cannot be a QSL. In this thesis I present published experiments I have performed on QSL candidate materials. By using muon spin rotation (μSR) and AC magnetic susceptibility I have evaluated the ground states of several candidates for the absence of long-range magnetic disorder and low-temperature spin-fluctuations. For the systems which order or spin-freeze, my research provided key knowledge to the field of frustrated magnetism. The systems I studied are as follows: The geometrically frustrated systems NaYbO2 and LiYbO2; the Kitaev honeycomb systems Cu2IrO3 and Ag3LiIr2O6; and the metallic kagome system KV3Sb5. Each of these systems brought new physics to the field of frustrated magnetism. NaYbO2 is a promising QSL candidate. LiYbO2 harbors an usual form of spiral incommensurate order that has a staggered transition. Cu2IrO3 has charge state disorder that results in a magnetically inhonogenious state. Ag3LiIr2O6 illustrates the role structural disorder plays in disguising long-range magnetic order. And finally, KV3Sb5 isn’t conventionally magnetic at all; our measurements ruled out ionic magnetism and uncovered a type-II superconductor. Our measurements on KV3Sb5 stimulated further research into KV3Sb5 and it’s unconventional electronic states. / Thesis (PhD) — Boston College, 2022. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

The production and fabrication of semi-conductor core optical fibers was shown to be feasible and controllable. This was accomplished through the step sequence of fabrication and characterization of 4 fiber types, an experiment on controlling the grain length in the core and a simple model of the heat transfer during fabrication. Fibers were first made with a silicon core, followed by a phosphorous doped n-type silicon core, then a boron doped p-type silicon core, and a tellurium doped n-type gallium antimonide core. Characterization of the fibers was accomplished with energy dispersive spectroscopy (EDS) for compositional analysis, electron backscatter diffraction (EBSD) for crystal orientation and grain size, optical and electron microscopy for physical fiber quality and optical transmission for core optical quality. A model was developed to relate the heat transfer with the grain structure of the fiber core. All of the fibers fabricated had a polycrystalline core with either no detectable oxygen in the case of the silicon fibers or low amounts of oxygen diffusion into the core as in the case of the GaSb fibers. Fiber lengths ranged from 7 cm for the initial silicon fibers to 60 cm and outside diameters down to 100 µm for n and p type silicon fibers. Core diameters for all fiber types ranged from 10 – 200 µm depending on the fabrication parameters. Lengths of major grains in the core are dependent on the core diameter and the pulling speed. The grain lengths of the major grains in the core generally increase in length with an increase in core diameter. Grain lengths in all fibers are thought to be suitable for use in fabrication of electronic structures in the core region with even the smallest average grain length of around 300 µm. This grain structure satisfies the grain boundary requirements for fabrication of boundary free p-n junctions and other more complicated electronic structures. Small core diameter fibers had better physical quality with fewer cracks and longer continuous length than the larger core fibers. / Ph. D.

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