GOALI: Charge Transfer in Semi-Insulating GaN

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Technical Description: Although GaN is effectively used in lighting applications, some electronic devices require high resistivity material. The goal of this GOALI project is to investigate and understand charge transfer mechanisms among the defects used to achieve insulating GaN and to assess the influence of the intentional impurities on crystal quality. Specifically, electron paramagnetic resonance (EPR) spectroscopy is used to probe charge transfer between the intentionally added Fe impurities and intrinsic donors. The EPR measurements provide a fingerprint of the Fe and donor defects, and, combined with photo-excitation, are used to monitor various charge exchange processes. Additionally, several different charge states of the Fe impurity as well as other potential defect centers are probed with optical absorption spectroscopy, and overall crystal quality is assessed with x-ray diffraction. The experiments primarily address bulk Fe-doped substrates grown by hydride vapor phase epitaxy at Kyma Technologies, the industrial collaborator of this project. However, additional studies include comparisons with samples grown by other growth techniques, such as high pressure solution, and doped with different compensating impurities so that optimal growth parameters for stable insulating nitride substrates may be determined.Non-technical Description: The insights gained by directly probing defects in GaN provide input for improved growth techniques, so that high-quality, high-resistivity material needed for future power electronics can be realized. By interacting with the industrial collaborators, students gain a view of science not available in a classroom setting. Furthermore, a summer research experience with Kyma is being offered to one of the graduate students working on this research, and at least one seminar by a Kyma scientist is planned. Both are intended to introduce students to the practical issues associated with material growth and device development. At the pre-college level, the PI gives an afternoon presentation on colloquial topics related to GaN devices at the week-long high-school Physics Bridge workshop organized by a colleague in the department.