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Title: Optical Memory Effects in III-V Nitrides
Authors: Chang, Yun-Chorng
Advisors: KOLBAS, R. M., Chair
BEDAIR, S. M., Member
OSBURN, C. M., Member
MISRA, V., Member
MUTH, J. F., Member
Issue Date: 9-Jan-2002
Degree: PhD
Discipline: Electrical Engineering
Abstract: Optical memory effects in III-V Nitrides have been investigated. In order to have further understanding of this effect, qualitative and then quantitative measurements were performed to investigate this memory effect. A microscopic model consistent with most of the experimental observations was developed. Finally, verification of the model was performed.Experimental observations indicate that optical memory effects are flux-dependent effects, which require no lower power limit of the excitation source in order to produce them. Photoluminescence and cathodoluminescence studies indicate the yellow patterns are the result of increased yellow luminescence intensity from the sample. Heating up the samples can erase this memory effect. Blue luminescence, with an energy about 2.8 eV, is important in the explanation of the memory effect since it appears in the photoluminescence spectra of all the samples that exhibit memory effects. This leads to a model with two different transitions, yellow and blue luminescence, competing with each other to explain the memory effects. The blue luminescence is caused by electron transitions from a localized oxygen level to the deep isolated and hydrogenated gallium vacancies. Transitions from shallow silicon donor levels to the gallium vacancies result in the yellow luminescence. Intense ultraviolet light will remove hydrogen from the hydrogenated gallium vacancies and these vacancies will form complexes with neighboring oxygen atoms. These complexes will result in more yellow luminescence. Less blue luminescence and more yellow luminescence result in the yellow memory patterns observed. This model is consistent with most of the observations and several experiments strongly support this model. Potential applications for memory effects include optical data storage and optical signal processing. Further understanding of this effect could lead to the realization of all optical memory cells and could also be used to improve the quality of III-nitrides materials.
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