Site-Selective Optical and Magnetic Properties of Rare Earth Ion Doped Nitrides

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Technical: This project aims for greater understanding of Er-doped wide-bandgap refractory nitride materials (GaN; AlGaN). The approach utilizes CEES (combined excitation and emission spectroscopy) and CL (cathodoluminescence) techniques to study and assess defects and their detailed role in excitation processes through variation of defect types and concentrations. Dynamical processes will be explored by pump-probe reflectivity measurements in combination with time-resolved experiments, in which a subset of ions are excited resonantly while others are excited through injected electrons or by a UV laser. Additionally, rare earth ions will be used in connection with confocal and near-field optical spectroscopy as probes for intrinsic local fields utilizing their characteristic shifts and level splitting from Stark and Zeeman effects. Two issues are of particular interest: (1) the nature of carrier localization effects in AlGaN that are seen in the most efficient UV light emitters, and (2) the site-selective nature of ferromagnetism observed in rare earth doped GaN, and how the phase transition temperature, magnetization and other magnetic properties depend on the relative number of incorporation sites. Non-technical: The project addresses basic research issues in a topical area of electronic/photonic materials science with high technological relevance. Research and educational activities will be integrated with involvement of both graduate and undergraduates in the research program. The PI will continue to actively contribute to outreach workshops on advanced materials for K-12 through the Lehigh Science Outreach program. As part of this project the PI will initiate two new educational activities: (1) he will utilize the atom-like properties of rare earth ions in solids to develop laboratory experiments that serve as an add-on to the Modern Physics courses at Lehigh University. In this, he will collaborate with the Society of Physics Students (SPS) chapter at Lehigh University to create several 'just for fun' experiments that students can do outside the regular course schedules during evening hours; (2) in order to increase the involvement of minorities in science, the PI has established collaborations with two historically black colleges (Grambling, Hampton); undergraduates from these colleges will work on the project during the summer, as part of the Physics REU program at Lehigh University.