Collaborative Research: A search for novel efficient p-type nitride materials

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Non-technical Description: Gallium nitride (GaN) semiconductor is a key component in bright light-emitting diodes (LEDs) used in solid-state lighting and other electronics applications. Most of these devices rely on so-called p-type GaN, a material with added impurities, which greatly improve its properties. In addition, exciting opportunities in optoelectronics currently emerge in development of a related material, p-type AlGaN. This is potentially groundbreaking since it will pave the way toward bright ultraviolet (UV) LEDs that can be used in numerous energy efficient applications, including air and water purification, phototherapy, gas sensing, plant growth lighting, and UV curing. The integrated experiment/theory research project is aimed at realizing new efficient conductive p-type GaN and AlGaN semiconductor materials. Adding beryllium (Be) impurity to GaN and AlGaN is expected to result in significantly improved p-type conductivity of these materials, leading to dramatic improvement of UV LED efficiency. Students, including those from underrepresented groups, have the opportunity to gain hands-on experience with state-of-the-art material deposition, optical spectroscopy experiments, and theoretical calculations. The project also builds a strong foundation for research and education in a relatively small Physics Department at Virginia Commonwealth University. Technical Description: The project focuses on growth of Be-doped GaN and AlGaN and fundamental studies of point defects in these materials. Analysis of photoluminescence from Be-doped GaN indicates that Be is the shallowest acceptor in GaN, yet achievement of p-type conductivity is still a challenging task, because a variety of point defects are formed during material growth. This collaborative research involves first-principles calculations of microscopic properties of Be and related defects in GaN and AlGaN, growth of Be-doped GaN and AlGaN by metalorganic chemical vapor deposition method, use of ion implantation, thermal annealing, and detailed experimental studies, primarily with photoluminescence and Kelvin probe methods. The roles of growth conditions (temperature, pressure, gas ambient), co-doping with Si and Mg, delta doping techniques, use of surfactants, various thermal annealing approaches are investigated to achieve conductive p-type materials. An in-depth and comprehensive study of the properties and behavior of Be and other defects in GaN and AlGaN by using advanced experimental and theoretical approaches is essential to gain a basic understanding of point defects in semiconductors, the mechanisms of radiative and nonradiative recombination, and possible growth pathways for realizing the efficient p-type materials. Furthermore, the accuracy of current approaches in solid-state theory is critically examined through direct experimental verification.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.