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Thin-film transistors (TFTs) are primarily used as a switching element in liquid crystal displays. Currently, amorphous silicon is the dominant TFT technology for displays, but higher performance TFTs will become necessary to enable ultra-definition resolution high-frequency large-area displays. Amorphous zinc tin oxide (ZTO) TFTs were fabricated by RF magnetron sputter deposition. In this study, the effect of both deposition and post annealing conditions have been evaluated in regards to film structure, composition, surface contamination, and device performance. Both the variation of oxygen partial pressure during deposition and the temperature of the post-deposition annealing were found to have a significant impact on TFT properties. X-ray diffraction data indicated that the ZTO films remain amorphous even after annealing to 600° C. Rutherford backscattering spectrometry indicated that the Zn:Sn ratio of the films was ~1.7:1 which is slightly tin rich compared to the sputter target composition. X-ray photoelectron spectroscopy data indicated that the films had significant surface contamination and that the Zn:Sn ratios changed depending on sample annealing conditions. Electrical characterization of ZTO films using TFT test structures indicated that mobilities as high as 17 cm² V⁻¹ s⁻¹ could be obtained for depletion mode devices. It was determined that the electrical properties of ZTO films can be precisely controlled by varying the deposition conditions and annealing temperature. It was found that the ZTO electrical properties could be controlled where insulating, semiconducting and conducting films could be prepared. This precise control of electrical properties allowed us to incorporate sputter deposited ZTO films into resistive random access memory (RRAM) devices. RRAM are two terminal nonvolatile data memory devices that are very promising for the replacement of silicon-based Flash. These devices exhibited resistive switching between high-resistance states to low-resistance states and low-resistance states to high-resistance states depending on polarity of applied voltages and current compliance settings. The device switching was fundamentally related to the defect states and material properties of metal and insulator layers, and their interfaces in the metalinsulator-metal (MIM) structure. / Graduation date: 2012 / Access restricted to the OSU Community at author's request from Jan. 6, 2012 - Jan. 6, 2013

Nesta tese apresentamos os estudos de magnetotransporte em poços quânticos largos,\\\\ estreitos e triplos em campos magnéticos baixos. Dependendo dos estudos desejados, me-\\\\dimos a magnetoresistência em regime linear e não linear e sob a aplicação de corrente AC, irradiação de microondas e em gradiente de temperatura ao longo das amostras. Relatamos a observação de efeitos não lineares de corrente alternada em oscilações magneto-inter-sub-bandas de poços quânticos triplos. A oscilação MIS em sistemas de poços quânticos individuais e duplos e também os efeitos não lineares devido à corrente contínua foram estudados antes nestes sistemas. Nossos resultados são explicados de acordo com um modelo generalizado baseado na parte de não equilíbrio da função de distribuição de elétrons. A magnetorresistência não local sob irradiação de microondas é também estudada nesta tese. Os resultados obtidos proporcionam evidências para uma corrente de estado de borda estabilizada por irradiação de microondas, devido às ressonâncias não lineares e foram descritas por um modelo baseado em dinâmica não linear e mapa padrão de Chirikov. Finalmente, observamos uma correlação estreita entre as oscilações de resistência e oscilações de tensão de arraste do fônon induzidas por irradiação de microondas em um sistema bidimensional de eletrons sob campo magnético perpendicular. A influência da resistividade de dissipação modificada por microondas na tensão de arraste do fônon perpendicular ao fluxo de fônons pode explicar nossas observações. Além disso, características nítidas observadas na tensão de arraste do fônon sugerem que os domínios de corrente associados a estes estados podem existir na ausência de condução DC externa. / In this thesis, we present the studies of magneto-transport in narrow , wide and triple quantum wells in low magnetic fields. Depending on the desired studies, we have measured the magneto-resistance both in linear and nonlinear regimes and under the application of AC current, microwave irradiation and temperature gradient along the samples. We have reported the observation of nonlinear effects of AC current on magneto-inter-sub-band oscillations (MIS) of triple quantum wells (TQWs). The MIS oscillations in single and double quantum well system and also nonlinear effects due to DC current have been studied before in these systems. Our results are explained according to a generalized model based on non-equilibrium part of electron distribution function. The nonlocal magneto-resistance under microwave irradiation is also studied within this thesis. The obtained results provide evidence for an edge-state current stabilized by microwave irradiation due to nonlinear resonances and have been described by a model based on the nonlinear dynamics and Chirikov standard map. Finally, we have observed the phonon-drag voltage oscillations correlating with the resistance oscillations under microwave irradiation in a two-dimensional electron gas in perpendicular magnetic field. The influence of dissipative resistivity modified by microwave on phonon-drag voltage perpendicular to the phonon flux can explain our observations. Moreover, sharp features observed in phonon drag voltage suggest the current domains associated with these states can exist in the absence of external DC driving.

This dissertation summarizes three research projects related to microwave radiation induced electron transport properties in the GaAs/AlGaAs two dimensional electron systems. In chronological order, the projects are: a microwave reflection and electron magneto-transport correlation study, the combined microwave power and polarization dependence on microwave radiation induced magneto-resistance oscillations study, and a comparative study about the effect of circularly polarized and linearly polarized microwaves radiation on magneto-resistance oscillations induced due to the microwave. These three research projects experimentally address many interesting issues in the non-equilibrium low dimensional electron transport under microwave irradiation and provide potential applications of utilizing microwave radiation induced magneto-resistance oscillations in two dimensional electron systems as a method to detect different qualities of microwaves or terahertz waves.

Ce travail de cette thèse présente les études sur l'influence du nouveau dégrée de liberté quantique, causé par le couplage tunnel entre les couches, sur les propriétés de transport des multi-puits quantiques dans un champ magnétique, à basse température, et sous irradiation micro-ondes. De nouvelles oscillations de résistance sont observées dans les systèmes d’électrons bi- et multicouches. Elles résultent d'une interférence entre les oscillations entre les sous-bandes et les oscillations induites par les micro-ondes. Des états à résistance nulle apparaissent lorsque les systèmes bicouches de haute qualité sous irradiation micro-ondes même en présence d’une diffusion additionnelle. Le mécanisme inélastique de la photorésistance est la contribution dominante à basses températures et sous un champ électronique modéré. Ce modèle confirme l'intégrité des estimations théoriques pour le temps de relaxation inélastique et mène à une explication satisfaisante de la photorésistance dans les systèmes d’électrons bi-et multicouches. Dans un champ magnétique intense, la suppression de l’effet tunnel entre les couches provoque des nouveaux états corrélés à cause d’une interaction électron-électron entre les différentes couches. Dans cette thèse, les systèmes électroniques tricouches, formés par de triples puits quantiques révèlent de nouveaux états de l’effet Hall Quantique fractionnaire si l’effet tunnel est supprimé par une composante parallèle du champ magnétique aux très basses températures (mK). / This work is devoted to the investigation of the influence of the additional quantum degree of freedom caused by tunnel coupling on transport properties of multilayer electron systems in magnetic fields, at low temperatures and under microwave excitation. Microwave-induced resistance oscillations in bi- and multilayer electron systems are the consequence of an interference of magneto-intersubband and microwave-induced resistance oscillations which leads to peculiar oscillations in magnetoresistance. High-quality bilayer systems exposed to microwave irradiation exhibit zero-resistance states even in the presence of intersubband scattering. The inelastic mechanism of microwave photoresistance is found to be the dominant contribution at low temperatures and moderate microwave electric field. This model confirms the reliability of theoretical estimates for the inelastic relaxation time and leads to a satisfactory explanation of photoresistance in bi- and multilayer electron systems. In high magnetic fields, the suppression of tunnelling between layers causes new correlated states owing to electron-electron interaction in neighboured layers. In this thesis, trilayer electron systems formed by triple quantum wells reveal new fractional quantum Hall states if tunnelling is suppressed by a parallel component of the magnetic field at mK temperatures.

Nesta tese apresentamos os estudos de magnetotransporte em poços quânticos largos,\\\\ estreitos e triplos em campos magnéticos baixos. Dependendo dos estudos desejados, me-\\\\dimos a magnetoresistência em regime linear e não linear e sob a aplicação de corrente AC, irradiação de microondas e em gradiente de temperatura ao longo das amostras. Relatamos a observação de efeitos não lineares de corrente alternada em oscilações magneto-inter-sub-bandas de poços quânticos triplos. A oscilação MIS em sistemas de poços quânticos individuais e duplos e também os efeitos não lineares devido à corrente contínua foram estudados antes nestes sistemas. Nossos resultados são explicados de acordo com um modelo generalizado baseado na parte de não equilíbrio da função de distribuição de elétrons. A magnetorresistência não local sob irradiação de microondas é também estudada nesta tese. Os resultados obtidos proporcionam evidências para uma corrente de estado de borda estabilizada por irradiação de microondas, devido às ressonâncias não lineares e foram descritas por um modelo baseado em dinâmica não linear e mapa padrão de Chirikov. Finalmente, observamos uma correlação estreita entre as oscilações de resistência e oscilações de tensão de arraste do fônon induzidas por irradiação de microondas em um sistema bidimensional de eletrons sob campo magnético perpendicular. A influência da resistividade de dissipação modificada por microondas na tensão de arraste do fônon perpendicular ao fluxo de fônons pode explicar nossas observações. Além disso, características nítidas observadas na tensão de arraste do fônon sugerem que os domínios de corrente associados a estes estados podem existir na ausência de condução DC externa. / In this thesis, we present the studies of magneto-transport in narrow , wide and triple quantum wells in low magnetic fields. Depending on the desired studies, we have measured the magneto-resistance both in linear and nonlinear regimes and under the application of AC current, microwave irradiation and temperature gradient along the samples. We have reported the observation of nonlinear effects of AC current on magneto-inter-sub-band oscillations (MIS) of triple quantum wells (TQWs). The MIS oscillations in single and double quantum well system and also nonlinear effects due to DC current have been studied before in these systems. Our results are explained according to a generalized model based on non-equilibrium part of electron distribution function. The nonlocal magneto-resistance under microwave irradiation is also studied within this thesis. The obtained results provide evidence for an edge-state current stabilized by microwave irradiation due to nonlinear resonances and have been described by a model based on the nonlinear dynamics and Chirikov standard map. Finally, we have observed the phonon-drag voltage oscillations correlating with the resistance oscillations under microwave irradiation in a two-dimensional electron gas in perpendicular magnetic field. The influence of dissipative resistivity modified by microwave on phonon-drag voltage perpendicular to the phonon flux can explain our observations. Moreover, sharp features observed in phonon drag voltage suggest the current domains associated with these states can exist in the absence of external DC driving.