Technical: This Focused Research Group project, funded jointly by the Electronic and Photonic Materials (EPM) and Ceramics (CER) Programs, encompasses a systematic interdisciplinary effort combining physics, materials science and electrical engineering to elucidate interconnections among the structural, electronic and optical properties of the transparent conductor gallium oxide, Ga2O3, with emphasis on intrinsic and extrinsic defects, interface chemistry, and dimensionality. Ga2O3 is transparent throughout the solar spectrum and into the near ultraviolet (UV), with a band gap of 4.9 eV (wavelength ~ 250 nm), but can be made conductive through doping (e.g., Si or Sn), by processing to create intrinsic defects (e.g. oxygen vacancies or interstitials), or through deep-UV photoabsorption. The anisotropic crystal structure of beta- Ga2O3 contains intrinsic, one-dimensional, open channels, and can be fabricated in structures with arbitrary dimensionality - 3D bulk crystals, 2D films, quasi-1D nanobelts, 1D nanowires and 0D nanospheres - as well as maintain that structure when alloyed with Al2O3 over a wide concentration range. Ga2O3 can undergo resistive switching (RS) with appropriate processing, but unlike more commonly considered transition metal oxides, gallium remains Ga3+ during creation of oxygen vacancies and/or interstitials, placing it in a different class of RS materials. This project will address key issues related to Ga2O3 that are not currently well understood: the interplay between ionic and electronic conductivity in Ga2O3, the nanoscale processes by which surface and interface reactions induce conductivity changes, and the role of the intrinsic channel structure in governing these properties. Ga2O3 has been proposed for several applications, including a "solar-blind" transparent conductor, a resistive switching memory element, an UV only photodetector, a chemical sensor, and a catalysis substrate. This research will contribute to mechanistic understanding of the conductivity and interface reduction-oxidation reactions that govern the operation of these prototype device structures, enabling refinement and enhancement of their function.
This project addresses workforce development at several levels. Graduate students will be actively involved in multidisciplinary research that spans science and engineering, and involves collaboration among academic, industrial and government laboratories in the US and Japan. They will develop key skills across several arenas that will enhance their career opportunities: materials synthesis, table-top sample characterization, synchrotron and other user-facility-based measurements, theoretical modeling, and proposal writing (for user facility access), as well as analytical and both oral and written communication skills as they process, interpret and present their research findings. The project also includes well-defined activities to increase interactions with populations that are frequently unaware of research activities at the University of Washington. Established connections with a local high school at which the majority of students don't typically aim for college will be expanded through active mentoring of high school students to perform photocurrent measurements of oxide samples grown under this proposal, summer research collaboration with the high school teacher who directs the science and robotics clubs there, as well as visits to classrooms to discuss both our science and students career and educational options.
