Infrared Quantum Materials Based on Scandium-Containing III-Nitrides

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Nontechnical descriptionThis project is developing new technologically useful materials by incorporating a rarely used metal (scandium) into traditional semiconductors. This combination has unique light emitting and detecting capabilities with broad benefits to society including novel devices for medical imaging and solar cells. The research aims to understand, control, and adjust the atomic arrangement of these new materials to maximize light absorption in the invisible infrared range. The project also explores the effect of atomic imperfections in the semiconductors on the movement of free electrical charge. This program also links the research with the educational goal of increasing learning opportunities for students of all ages, inside and outside the traditional classroom. The investigators and students involved in this project participate in outreach activities organized either in-house or at local schools to increase exposure of K-12 students and the general public to modern scientific topics in materials science in a fun, project-oriented environment. Lesson plans are designed and experimental demonstrations of basic optical properties of matter are built for the middle-school summer camp “Physics Inside Out” at Purdue. To maximize impact at the high-school level, the activities engage teachers in summer research. In particular, the teachers are developing inquiry-based lesson plans incorporating concepts related to quantum science into the high-school curriculum to fulfill Indiana standards. The researchers also organize a hands-on workshop with take-home materials for the annual meeting of the Hoosier Association of Science Teachers.Technical descriptionThis project sets the foundation for a novel type of infrared materials using optical transitions between quantized states in the conduction band of nitride semiconductors incorporating the group IIIB transition-metal scandium. These semiconductors have unique electronic properties that make them suitable for advancing the functionality of semiconductor optoelectronic devices into spectral ranges currently inaccessible with other material systems. The innovative approach employs an emergent optoelectronic material, the wurtzite phase of Sc-Al-nitride that is lattice-matched to GaN, to mitigate strain-related issues that have impeded progress of nitride optoelectronics into the infrared so far. The research effort is interdisciplinary and involves material design and growth, plus structural and optical characterization. Polar and nonpolar ScAlN/GaN heterostructures are designed using extensive band-structure calculations. To achieve maximum material purity and monolayer-control of the atomic structure, the Sc-containing materials are grown by plasma-assisted molecular beam epitaxy on high quality quasi-bulk GaN substrates. The decisive task is to identify the epitaxial growth conditions that satisfy the most stringent requirements imposed by near-infrared optical processes. In order to correlate microstructure with optical and electronic properties, the structure of the semiconductor materials is comprehensively characterized with high-resolution x-ray diffraction, advanced transmission electron microscopy, and atom probe tomography. The band structure of the materials is probed experimentally with Fourier transform infrared spectroscopy and photoluminescence. The growth of these emergent materials advances the state-of-the-art in transition-metal nitride epitaxy. Uncharted mechanisms of material growth on polar and non-polar GaN substrates are scrutinized. This research also contributes to the knowledge base of the physics of infrared optical transitions. These infrared materials are expected to enable optoelectronics with functionality unmatched by current technologies. Moreover, the novel class of Sc-containing semiconductors benefit other applications such as high-electron mobility transistors, ultraviolet, thermoelectric, piezoelectric, and plasmonic devices.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.