Technical: This project will advance the academic and public understanding of the principles of optical/electronic materials used for photonics through laboratory research and educational outreach. Wide bandgap III-Nitride semiconductors span the ultraviolet-visible-near infrared spectrum finding energy efficient applications in ultraviolet-visible light sources and detectors. Self-assembled Nitride nanowires increase the design flexibility in heterostructures due to high tolerance to lattice mismatch. This project will achieve new types of optical and electrical functionality in nanowire heterostructures for advanced high efficiency photonics. In bulk, polarization charge and bandgaps in GaN, AlN, and InN cannot be maintained in a single heterostructure without generating large numbers of dislocations due to strain relaxation. Nanowires sidestep the constraint of epitaxial strain making possible extreme energy landscapes for electrons and holes in graded AlGaN and InGaN heterostructures, while maintaining single crystal defect-free active regions. A remarkable array of heterostructures are possible exhibiting large built-in electric fields due to polarization charge that separate electrons and holes with high speed and efficiency, properties that enable high speed photodetectors covering a broad range in energy. Polarization grading will also be used to achieve impurity free p and n type doping in nanowires, which sidesteps the problem of impurity doping in nanostructures, and will be used to demonstrate a dopant-free pn-junction LED. To achieve these heterostructures, a systematic mapping of the growth phase diagram of molecular beam epitaxy growth of self-assembled GaN and InN nanowires on Si (111) for arbitrary selection of nanowire diameter and density will be investigated, and a suite of structural, optical, and electronic techniques will be employed, including SEM, Z-contrast TEM, XRD, time-resolved photoluminescence, electroluminescence, nanowire transport, and trap spectroscopy to examine fundamental transport and optical properties as they relate to nanowire structure and polarization charge/doping phenomena.
Controlling how atoms combine to form nanoscale crystals of semiconductors allows efficient conversion of light to electricity, and vice versa. However, even scientifically inclined students and teachers are largely unaware of the foundations of remarkable solar conversion, lighting, and display technologies, and completely unaware of the science of crystal growth. To address this shortfall, tutorials and lab demonstrations geared toward high school students will be integrated into the extensive outreach infrastructure at Ohio State, including open houses and summer camps that target minority students and women. A series of day long and summer camp events in the department of Materials Science and Engineering will take part in a hands-on tutorial/lab demonstration on materials for electro-optical energy conversion. The same tutorial will be remotely beamed to high school students around the country through the Electronics Experts program at the COSI science museum, which also provides a framework for tutorial development, and evaluation.
