Ultrawide Bandgap Gallium Oxide: Fundamental Understanding From Materials Synthesis to Devices

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Nontechnical description: Gallium oxide is a promising material for high-voltage, high-temperature, and high-frequency components in radar and communication systems, wind turbines, and rail traction. Its band gap of ~4.9 electron volts and estimated high breakdown voltage significantly goes beyond currently developed materials, such as GaN and 4H-SiC, while still presenting semiconductor properties. This research focuses on the theoretical modeling of gallium oxide for predicting its fundamental material properties, and the experimental synthesis of this material by using high purity metallic gallium and oxygen as sources. The project aims to produce high quality gallium oxide and to advance the fundamental understanding of this emerging material. Theoretical studies of the fundamental properties of imperfections in the material provides guidance for experimental material growth and material characterization. The development of strategies for synthesis of this material and progress in understanding their properties contribute an important body of work to the research infrastructure. A successful execution of this research is expected to provide a knowledge foundation to power electronics industry with positive impacts on the US economy. This project trains two graduate students in the areas of advanced semiconductor materials synthesis, material characterization, first-principles modeling and device technologies. The research is integrated with educational activities and outreach to benefit the broader community. Technical description: The key research goal is to identify and address the fundamental material challenges of synthesizing high quality ultra-wide-band-gap (UWBG) gallium oxide to advance the next generation high power electronics and short wavelength optoelectronics. The synthesis and fundamental understanding of gallium oxide is still very much in its infancy. The exploration of native defects such as vacancies, interstitials, antisites, and impurities or intentional dopants is expected to be complex because three different oxygen sites and two different gallium sites need to be considered. The research team investigates these problems by combining first-principles modeling with a proposed novel synthesis method for achieving high quality epitaxial gallium oxide films. Specifically, the research efforts include: (i) a low pressure chemical vapor deposition approach to grow gallium oxide; (ii) reduce defects and improve material quality by growing gallium oxide on off-axis substrates; (iii) calculations of the energy of formation and defect levels for point defects, candidate dopants and defect complexes and their experimental signatures, such as electron paramagnetic hyperfine and g-tensors and optical properties; (iv) investigate the crystal defects on electrical properties of gallium oxide. This project provides fundamental understanding of electronic structure, phonons, transport, defects and growth optimization. The theoretical studies will assist in identifying the chemical nature of specific defect levels and thereby will provide guidance for experimental material synthesis and material characterization. The results from this project will fill the knowledge gap in this field, and build a foundation for future applications of this material system.