Understanding p-Type Doping in GaN: the Role of Mg

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Technical: This project aims to understand the chemistry, structure, and optical sensitivity of the Mg impurity used to produce p-type GaN so that the present limitations to achieve a high dopant density can be understood and new approaches to doping may be realized. It employs electron paramagnetic resonance (EPR) spectroscopy to probe the optical sensitivity and chemical reactivity of the Mg impurity in GaN. Specifically, changes in the thermal annealing behavior between films grown with the typical Mg concentration used in the present day devices and those grown by methods intended to achieve high hole densities are monitored. Further, the research involves a new method to probe the Mg impurity: time-dependent photo-EPR. Analysis of such data could provide information about charge exchange between Mg and other defects, which will likely change as Mg concentration is increased. Additional experiments include high frequency EPR available at the National High Magnetic Field Laboratory. The high frequency experiments may reveal the local symmetry of the impurity and the role of strain. Overall, the project is designed to investigate factors that limit effective p-type doping and may provide direction to maximize hole density and conductivity of GaN.Non-technical: The project addresses basic research issues in a topical area of materials science with high technological relevance. A success of the research project could contribute to development of better light emitting diodes and electronic devices. The PI, who has mentored many undergraduates in science, mathematics and engineering, teaches a sophomore-level Science and Technology Honors seminar at the University of Alabama, which includes a section on future lighting technologies and efficient high power/high frequency electronic devices. The collaboration of the Honors students with PhD candidates in the PI's laboratory will foster a sense of interdisciplinary research essential for success complement to their formal education.