Matching Items (2)
Description
III-nitride alloys are wide band gap semiconductors with a broad range of applications in optoelectronic devices such as light emitting diodes and laser diodes. Indium gallium nitride light emitting diodes have been successfully produced over the past decade. But the progress of green emission light emitting devices has been limited by the incorporation of indium in the alloy, mainly due to phase separation. This difficulty could be addressed by studying the growth and thermodynamics of these alloys. Knowledge of thermodynamic phase stabilities and of pressure - temperature - composition phase diagrams is important for an understanding of the boundary conditions of a variety of growth techniques. In this dissertation a study of the phase separation of indium gallium nitride is conducted using a regular solution model of the ternary alloy system. Graphs of Gibbs free energy of mixing were produced for a range of temperatures. Binodal and spinodal decomposition curves show the stable and unstable regions of the alloy in equilibrium. The growth of gallium nitride and indium gallium nitride was attempted by the reaction of molten gallium - indium alloy with ammonia at atmospheric pressure. Characterization by X-ray diffraction, photoluminescence, and secondary electron microscopy show that the samples produced by this method contain only gallium nitride in the hexagonal phase. The instability of indium nitride at the temperatures required for activation of ammonia accounts for these results. The photoluminescence spectra show a correlation between the intensity of a broad green emission, related to native defects, and indium composition used in the molten alloy. A different growth method was used to grow two columnar-structured gallium nitride films using ammonium chloride and gallium as reactants and nitrogen and ammonia as carrier gasses. Investigation by X-ray diffraction and spatially-resolved cathodoluminescence shows the film grown at higher temperature to be primarily hexagonal with small quantities of cubic crystallites, while the one grown at lower temperature to be pure hexagonal. This was also confirmed by low temperature photoluminescence measurements. The results presented here show that cubic and hexagonal crystallites can coexist, with the cubic phase having a much sharper and stronger luminescence. Controlled growth of the cubic phase GaN crystallites can be of use for high efficiency light detecting and emitting devices. The ammonolysis of a precursor was used to grow InGaN powders with different indium composition. High purity hexagonal GaN and InN were obtained. XRD spectra showed complete phase separation for samples with x < 30%, with ~ 9% indium incorporation in the 30% sample. The presence of InGaN in this sample was confirmed by PL measurements, where luminescence from both GaN and InGaN band edge are observed. The growth of higher indium compositions samples proved to be difficult, with only the presence of InN in the sample. Nonetheless, by controlling parameters like temperature and time may lead to successful growth of this III-nitride alloy by this method.
ContributorsHill, Arlinda (Author) / Ponce, Fernando A. (Thesis advisor) / Chamberlin, Ralph V (Committee member) / Sankey, Otto F (Committee member) / Smith, David J. (Committee member) / Tsen, Kong-Thon (Committee member) / Arizona State University (Publisher)
Created2011
Description
This thesis examines heritage language learning and loss, and revitalization. It stems from my initial interests in Indigenous language revitalization and sustainment, bilingual education, and specifically dual language education in the United States. In this thesis, I describe my inquiry journey through narratives of the significant experiences and people I met and the scholarship I engaged in, particularly through visiting Keres Children’s Learning Center at Cochiti Pueblo, New Mexico, and attending the La Cosecha Dual Language Education conference in Santa Fe, New Mexico. In these narratives, I also reflect on what I have learned, how I was personally impacted by what I was learning and my thoughts and ideas about particular issues. These narratives helped me gain a deeper understanding of and expand my knowledge of heritage learning, bilingual education, dual language education and critical issues of language development and promotion (or non-promotion) in our country’s schools and families. Equally important is the knowledge I gained about dual language pedagogy and its critical importance to language revitalization programs serving Indigenous children, and their families and communities. I begin my thesis with a review of literature followed by a description of my methods and then move on to my narratives of significant learning moments, chronologically, and then summarize my key findings. I end with, ironically yet crucially with the most important lesson I learned through my inquiry journey—an understanding of my linguistic self.
This thesis examines the questions of
1. To become a Dual Language Education expert, researcher, or scholar, what does it take?
2. In what ways can a non-Native help Indigenous communities engaged in indigenous language revitalization and sustainment (ILRS)? What would they need to learn or know?
Some significant findings of my thesis work include
1. The strength, versatility, and challenges of the dual language education model in a national context
2. Culturally-sustaining pedagogy and strategies for adapting lessons to local culture
3. The centrality of tribal sovereignty and tribal control over the Indigenous language in order to grow and maintain an IRLS effort
4. Ways in which a non-Native can help an ILRS initiative
5. Respect for native communities’ right to say no to research
This thesis examines the questions of
1. To become a Dual Language Education expert, researcher, or scholar, what does it take?
2. In what ways can a non-Native help Indigenous communities engaged in indigenous language revitalization and sustainment (ILRS)? What would they need to learn or know?
Some significant findings of my thesis work include
1. The strength, versatility, and challenges of the dual language education model in a national context
2. Culturally-sustaining pedagogy and strategies for adapting lessons to local culture
3. The centrality of tribal sovereignty and tribal control over the Indigenous language in order to grow and maintain an IRLS effort
4. Ways in which a non-Native can help an ILRS initiative
5. Respect for native communities’ right to say no to research
ContributorsWelsh, Jacqueline Rose (Author) / Romero-Little, Eunice (Thesis director) / Tidwell, Jacqueline Hettel (Committee member) / School of International Letters and Cultures (Contributor) / W. P. Carey School of Business (Contributor) / Department of English (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05