Hydrogen in Zinc Oxide and Related Materials

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Technical: The proposed work will experimentally study Zinc oxide (ZnO) semiconductor that has attracted resurgent interest as a material for optoelectronic applications. While ZnO has many inherent advantages, the lack of control over dopants and defects presents an obstacle to the realization of practical devices. Reliable p-type conductivity, necessary for widespread applications, has been elusive. A key challenge is to introduce acceptors without being overwhelmed by compensating donors. Hydrogen plays a central role in acceptor doping of ZnO as well as unintentional n-type conductivity. The proposed work will focus on different forms of hydrogen in ZnO and related materials. Specifically, interstitial hydrogen donors, substitutional hydrogen donors, acceptor-hydrogen complexes, and vacancy-hydrogen complexes will be investigated with a range of experimental techniques. In this renewal proposal, research will be extended from ZnO to other oxide crystals, including tin oxide and strontium titanate. The proposed work will shed light on the origins of n-type conductivity in transparent conducting oxides, an open question with technological ramifications. The overall goal of the project is to investigate the behavior of hydrogen in ZnO and other oxide crystals. The research goals will promote a fundamental understanding of hydrogen in semiconductors. By extending the research to oxide crystals, the PI will investigate the possibility of universal behavior across different materials systems. The most "high-risk" goal is the achievement of p-type ZnO. Reliable p-type conductivity in ZnO would be transformative, opening up a range of novel applications. This renewal project builds on significant work by the PI's research group that resulted in high-impact publications, invited talks, Ph.D. dissertations, and undergraduate research experiences. Non-technical: The project addresses basic research issues in a topical area of materials science with technological relevance, and is expected to provide unique opportunities for graduate and undergraduate training in an interdisciplinary field. This research project is also expected to have broader impacts through the training of scientists in this research field, through the wide dissemination of the findings of this research through publications. The proposed educational activities will also benefit a range of students from elementary to Ph.D. In conjunction with the research part of this proposal, educational and outreach activities will encourage students from diverse backgrounds to enter fields related to materials science and solid-state physics.