Dynamics of Fundamental Optical Transitions in Gallium Nitride and Aluminum Gallium Nitride

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9528226 Lin This research project is targeted at the investigation of the dynamics of band-to-band exciton, and band-to-impurity transitions in GaN and AlGaN, including recombination lifetimes and quantum efficiencies, employing time-resolved photoluminescence spectroscopy measurements. These dynamic processes will be investigated in epitaxial layers, heterostructures, quantum wells, and artificially structured laser cavities under different conditions--temperature, excitation energy, intensity, and polarization. Fundamentally important physical quantities, including the free- and bound-exciton oscillator strengths which determine basic optical processes such as excitation, absorption, and recombination, will be measured. The effects of post-growth annealing, external fields, and alloy composition on the optical recombination dynamics will be included in the study. In addition, the dynamics of optical transitions will be investigated under conditions of optically-pumped stimulated emission and lasing to ascertain information regarding preferable optical transitions for laser applications as well as to provide model descriptions for gain mechanisms and quantum efficiencies in GaN lasers. %%% In wide bandgap semiconductor optical devices, such as UV emitters and UV-blue laser diodes, it is the dynamic processes of the fundamental optical transitions that predominantly determine their performance. The history of GaAs and ZnSe semiconductor laser development shows that understanding fundamental optical recombination dynamics is an important key to the understanding of laser activity. Additionally, an understanding of the dynamic processes of optical transitions provides new directions for improving material quality as well as being of great value in designing and optimizing optoelectronic devices. The research will contribute basic materials science knowledge at a fundamental level of technological relevance to several aspects of advanced photonics. Additionally, the knowledge and understandin g gained from this research project is expected to contribute in a general way to improving the performance of advanced devices and circuits used in computing, information processing, and telecommunications by providing a fundamental understanding and a basis for designing and producing improved materials. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area. ***