Native Point Defects, Electronically Active Impurities, and Plasmonics at ZnO Interfaces

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Technical Description: This research project examines the use of native point defects, degenerate doping, and nanostructures to advance the understanding of contact rectification, photon-plasmon coupling, and nanocontacts at ZnO interfaces. It builds on existing capabilities to identify the electrical activity of native point defects on a nanometer scale using optical and electronic techniques, to measure their effect on carrier densities and atomic dopant concentrations quantitatively, and to controllably introduce or suppress these native point defects using nanoscale surface science techniques. Native point defects have a major effect on ZnO Schottky barrier heights, and their interplay with dopant impurities influence plasmonic-resonance wavelengths in ZnO. Because ZnO exhibits a wide range of contact rectification with metals, it can serve to test the relative contributions of thermionic, tunneling, and hopping transport through ZnO-metal interfaces on both a macroscopic and nanometer scale, and the balance of physical mechanisms can be used to understand barriers to charge transport for a wide range of compound semiconductor junctions. The carrier densities influenced by native point defects can in turn alter the dielectric response of ZnO and thus the plasmon-resonance frequency used to couple light waves to ultrahigh frequency electronics. This project employs a combination of growth, plasma processing, and atomic indiffusion to control near-interface doping and native point defects on a nanometer scale for both barrier rectification and plasmonic coupling.Non-technical Description: Semiconductor defects are imperfections such as missing atoms or impurities in otherwise perfect semiconductor crystals. They can be electrically-active, altering the amount of electrical charge free to travel inside transistors, lasers, and other electronic devices. They can also serve as shortcuts for charge to move through electronic barriers usually designed to block such charge movement for transistor switching, charge storage, or carrier confined light emission. The influence of these defects in charge movement across ZnO interfaces provides a test bed to understand and control other semiconductors, an issue starting when these materials were first used for electronics. Their control can enable high carrier densities for transparent electronics such as heads-up displays and smart windows, high positive charge densities for lasers, and control of the coupling between light waves and electronic circuits at wavelengths important for telecommunications. The project provides training of graduate students, undergraduates, and high school women in both basic scientific laboratory techniques and advanced micro- and optoelectronic concepts. Students interact directly with international collaborators at the University of Oslo, Sweden, Aalto University, Finland, and CNRS / CRHEA, France. The project involves and supports women at the high school through the Columbus School for Girls' summer research internship program, building on NSF core funding with support from several Ohio State University institutions.