Nanoscale Characterization and Control of Native Point Defects in Metal Oxide Semiconductors and Device Structures
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| Language: | English |
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The Ohio State University / OhioLINK
2021
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| Online Access: | http://rave.ohiolink.edu/etdc/view?acc_num=osu1618838504594148 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-osu1618838504594148 |
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English |
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Condensed Matter Physics Materials Science Physics Solid State Physics Electrical Engineering Nanoscience Zinc Oxide Strontium Titanate Gallium Oixde Cathodoluminescence Dielectric Breakdown MBE SPS Native Point Defects Remote Plasma Neutron Irradiation Thermal Anneal Flash Sintering Surfaces and Interfaces |
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Condensed Matter Physics Materials Science Physics Solid State Physics Electrical Engineering Nanoscience Zinc Oxide Strontium Titanate Gallium Oixde Cathodoluminescence Dielectric Breakdown MBE SPS Native Point Defects Remote Plasma Neutron Irradiation Thermal Anneal Flash Sintering Surfaces and Interfaces Gao, Hantian Nanoscale Characterization and Control of Native Point Defects in Metal Oxide Semiconductors and Device Structures |
| author |
Gao, Hantian |
| author_facet |
Gao, Hantian |
| author_sort |
Gao, Hantian |
| title |
Nanoscale Characterization and Control of Native Point Defects in Metal Oxide Semiconductors and Device Structures |
| title_short |
Nanoscale Characterization and Control of Native Point Defects in Metal Oxide Semiconductors and Device Structures |
| title_full |
Nanoscale Characterization and Control of Native Point Defects in Metal Oxide Semiconductors and Device Structures |
| title_fullStr |
Nanoscale Characterization and Control of Native Point Defects in Metal Oxide Semiconductors and Device Structures |
| title_full_unstemmed |
Nanoscale Characterization and Control of Native Point Defects in Metal Oxide Semiconductors and Device Structures |
| title_sort |
nanoscale characterization and control of native point defects in metal oxide semiconductors and device structures |
| publisher |
The Ohio State University / OhioLINK |
| publishDate |
2021 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=osu1618838504594148 |
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AT gaohantian nanoscalecharacterizationandcontrolofnativepointdefectsinmetaloxidesemiconductorsanddevicestructures |
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1719490005013889024 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-osu16188385045941482021-10-16T05:25:16Z Nanoscale Characterization and Control of Native Point Defects in Metal Oxide Semiconductors and Device Structures Gao, Hantian Condensed Matter Physics Materials Science Physics Solid State Physics Electrical Engineering Nanoscience Zinc Oxide Strontium Titanate Gallium Oixde Cathodoluminescence Dielectric Breakdown MBE SPS Native Point Defects Remote Plasma Neutron Irradiation Thermal Anneal Flash Sintering Surfaces and Interfaces Metal oxides are of tremendous interest since they offer a wide span of physical properties, including tunable dielectric constants, ferroelectricity, ferromagnetism, ionic conductivity, catalytic activity, and superconductivity. They are critical materials for next generation electronic and energy-related applications including microelectronics, photovoltaic devices, data storage, magnetoelectronic, and fuel cells. While the versatility of metal oxides’ electronic applications is exciting, key to the performance of many of these applications is the electronic property-structure relationship. This relationship is fundamentally determined by the electronic structures of metal oxides, which are sensitive to compositions, impurities, surface/interfaces, grain boundaries and, in particular, defects. Defects are commonly believed to play a key role in metal oxides, where they can compensate free carriers, change carrier mobilities, “pin” Fermi level, and create trap states that initiate dielectric breakdown.This Ph.D. thesis describes my work using a combination of growth, processing, and characterization techniques to understand and control native point defects in metal oxides and their devices/nanostructures. By altering growth conditions, or implementing treatments including thermal anneal, plasma, mechanical strain, neutron irradiation, and high electric field, the atomic-scale processes to control electronic defects are characterized in nanometer scale by a complement of depth-resolved cathodoluminescence spectroscopy (DRCLS), Kelvin probe force microscopy (KPFM), surface photovoltage spectroscopy (SPS), and scanning electron microscope (SEM). It is evident in our results that the creation/passivation, redistribution, and configuration changes of defect complexes are critical in affecting the electronic properties of metal oxide materials, i.e., initiating the dielectric breakdown phenomenon. Based on four of my previously published journal articles, this thesis describes how the nanoscale characterization and control of defects in three metal oxide materials builds structure-property correlations and provide insights of defect engineering for novel functionalities.Flash sintered ZnO with orders of magnitude conductivity increase is investigated. DRCLS results reveal that the thermal runaway-induced formation of oxygen vacancies (V<sub>O</sub>) inside individual grains contributes to additional donors that increase conductivity within grains of the polycrystalline material. Hyperspectral imaging of granular cross sections shows nanoscale pathways of increased V<sub>O</sub> following thermal runaway, supporting a heating mechanism localized on a granular scale. These defects tend to form preferentially inside rather than at grain boundaries, localizing the dominant heating mechanism and further reduces the resistivity. For ZnO microwires, electromigration of defects was directly observed with systematically increasing external electric field.Laterally and depth-resolved cathodoluminescence spectroscopy (DRCLS) provided direct, nanoscale measurements of oxygen vacancy complex redistributions in Fe-doped and undoped SrTiO<sub>3</sub> (STO) films under electric field stress at elevated temperature associated with dielectric breakdown. Such migration driven by external electric field results in increased current leakage and lower thermal breakdown strength. DRCLS measurements through planar Pt electrodes after breakdown also reveal pronounced oxygen vacancy depletion at the Pt/SrTiO<sub>3</sub> interface as predicted theoretically. The deconvolution of spectral features provides methods to gauge the relative defect energetics of these gap states, corresponding to specific defect complexes, providing a tool to further understand conduction in mixed ionic conductors. Furthermore, similar electromigration of defects can also be induced by ultra-high electric field at room temperature, observed in a molecular beam epitaxy (MBE) grown SrTiO<sub>3</sub> thin film.DRCLS, temperature-dependent Hall effect measurements, surface photovoltage spectroscopy, and absorption spectroscopy are used to measure the effects of near-surface plasma processing and fluence dependent neutron irradiation on native point defects in β-Ga<sub>2</sub>O<sub>3</sub> and the associated changes of electrical properties. The spectral changes associated with removing or creating defects enables fundamental identification of one oxygen vacancy-related and two gallium vacancy-related energy levels in the β-Ga<sub>2</sub>O<sub>3</sub> band gap. Temperature-dependent Hall effect measurements show significant free carrier removal and mobility decrease after neutron irradiation. The correlations between defect profiles and electrical property changes vs. irradiation dose link these dominant electrically active native point defects in Ga<sub>2</sub>O<sub>3</sub> with their contributions to free carrier mobility, carrier density, and donor/acceptor depth profiles, further revealing their donor/acceptor electrical behavior and physical nature, consistent with the formation of compensating defects. Temperature-dependent forming gas (FG) anneals were performed to reverse the radiation-induced damage and carrier removal. Such evolution of defect concentrations and spatial distributions with neutron irradiation and FG anneals also reveal an interplay between specific defects to control electronic properties. 2021-10-07 English text The Ohio State University / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=osu1618838504594148 http://rave.ohiolink.edu/etdc/view?acc_num=osu1618838504594148 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |