EAGER: Formative Research on Contacts to Gallium-Oxide for Electronic and Optoelectronic Devices

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Title: Formative Research Program on Gallium Oxide Semiconductor Materials and Interfaces to Hasten the Development of Ultra-High Efficiency Electronics Non-Technical:The global energy crisis presents an urgency to develop ultra-high efficiency electronics for energy conversion and transport. Electricity accounts for more than a third of primary energy consumption in the U.S., and a large portion of that electricity is handled by power electronics. For example, power electronics are required for efficient electrical switching within the electrical grid, as well as for power supplies in hybrid electric vehicles and for power converters in Naval ship platforms and to integrate renewable energy systems into the electrical grid. In each of these applications, the power semiconductor device is the critical component that determines the energy conversion efficiency, in addition to the size and cost of the system. Because of its recent material (crystal) availability and its extreme properties, gallium oxide (Ga2O3) is a novel semiconductor material that is expected to yield superior devices for ultra-high efficiency electronics. Although there is strong interest in the U.S., to date, the vast majority of research and development (R&D) on gallium oxide has been conducted in Japan. This research project is designed to hasten the development of ultra-high efficiency electronics (especially power devices) based on gallium-oxide materials and interfaces and to establish a foundation for R&D activities on gallium-oxide within the U.S. Ultimately, advances in power electronics will account for substantial gains in energy savings and an associated reduction in carbon emissions. As part of this program graduate and undergraduate students will receive training and develop professional skills needed to work in the semiconductor industry. Additional outcomes will include scientific outreach to middle and high school students and teachers, and conference sessions to inform and to help build R&D activities in this emerging field. Technical:Specifically, in this project researchers at Carnegie Mellon University will conduct a formative study focusing on the physics, chemistry, and processing conditions that determine the behavior of electrical contacts to doped Ga2O3 single crystal substrates and epitaxial layers. A number of devices based on Ga2O3, including Schottky diodes, MESFETs, and MOSFETs, have been demonstrated. However, as research on Ga2O3 as a wide bandgap semiconductor is in its very early stages, there is little understanding of how to control device relevant interfaces to this material. Specifically, this research will focus on (1) forming low resistivity ohmic contacts, informed by thermodynamic calculations and consideration of other physical and chemical properties, and (2) characterizing Schottky diodes for a wide range of metals on different crystal orientations of Ga2O3 and comparing the Schottky barrier heights with predicted values. Knowledge of the effects of metal workfunctions, crystal orientation, interfacial reactions, and processing conditions on the contact properties will serve as a platform to enable informed designs that device engineers can use to achieve optimized devices based on Ga2O3, and, potentially, on alloys and heterostructures of (Al,Ga,In)2O3 materials in the future.