CAREER: Revealing the Fundamental Mechanisms Behind the Dislocation-Induced Electronic States in III-V Semiconductors

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Nontechnical AbstractIn nearly any material, from the steel in bridge girders to the silicon in computer chips, it is the imperfections, or defects, that dictate critical aspects of its properties; sometimes these defects are intentional and helpful, sometimes they are unintended and harmful. Similarly, for nearly every type of defect, the specific reason for these effects can be traced down to a basic set of questions: What atomic species are involved? And how are they bonded to each other? If one can answer these questions, then one can better figure out how to either harness or mitigate defects. In the world of electronics, the growing need for new materials and technologies with higher performance, broader range of useful functions, and better reliability often drives scientists and engineers away from the limited palette of traditional materials and towards various combinations of different materials, which frequently possess fundamental dissimilarities. However, this approach can lead to the formation of detrimental defects. For the kinds of semiconductors that are used to create many vital technologies, including LEDs, lasers, solar cells, infrared sensors, high-power/speed transistors, and more, the atomic-scale nature of many defects remain a mystery. Therefore, this project seeks to identify the atomic structures of important defects and understand how they degrade the parent materials’ electronic and optical properties. Knowing this, researchers can figure out how to get around the challenges caused by defects, and perhaps even find new, beneficial uses for them. To further broaden the overall impact of this project, the principal investigator is working to combine this new science with existing knowledge to develop fresh and exciting course curricula, while the entire research team will share their expertise by creating highly accessible experimental methods training videos. Furthermore, the team is engaging with the local community through inclusive outreach events to help participants, children and adults alike, discover the connections between fundamental semiconductor materials properties, like those under investigation in this project, and the operation of the vast range of devices that they use throughout their day-to-day lives, igniting and encouraging the imaginations and interests of the new generations of diverse individuals that will not only contribute to fields of science and engineering, but will serve as positive influences to society.Technical AbstractDislocations within III-V semiconductors commonly arise as a result of dissimilar (e.g. lattice/symmetry mismatched) materials integration, and lead to detrimental sub-bandgap electronic defect levels that severely limit the usefulness of such materials systems. However, the fundamental, atomic-scale structure of III-V dislocations (especially the core), and thus the specific source of said defect levels, largely remains a mystery. The goal of this project is to fill this critical knowledge gap by testing the hypothesis that the characteristic defect levels resident at III-V dislocations can be directly attributed to specific, atomic-scale structural features. Employing a novel, correlative characterization framework of optoelectronic and structural spectroscopies and microscopies, with resolutions spanning from the macroscale to the atomic, the researchers are identifying the specific elemental species and bonding configurations that result in detrimental electronic defect levels. By combining this analysis with well-controlled sample epitaxy, they will further determine how these defect structures, and their associated properties, are impacted by the alloy composition, bandgap, and doping of the host material. Ultimately, this research is helping to build and support a true bottom-up compound semiconductor materials and process design approach, with defect mitigation as an achievable target, that is particularly valuable in applications where dissimilar integration is needed.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.