GOALI: Zintl Engineering of Epitaxial Ceramic Films on Gallium Nitride

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This project is jointly funded by the Electronic and Photonic Materials (EPM) and Ceramic (CER) Programs in the Division of Materials Research. NON-TECHNICAL DESCRIPTION:Silicon has been the substrate of almost all microelectronic devices for the semiconductor industry over the last several decades. Motivated by the need for faster device speeds, the industry is considering compound semiconductors, such as gallium nitride, which have higher electron mobility. Accordingly, new dielectric layer materials that enable gallium nitride-based electronic devices are needed. This research project is exploring approaches to growing crystalline rare earth oxide films on gallium nitride that are well-matched to the crystal lattice of gallium nitride and make gallium nitride a viable substrate. Because gallium nitride and the rare earth oxides have different types of chemical bonding, this research is exploring interfacial layers that bridge the bonding types and force the oxide to grow as a two-dimensional layer. The partnership between academic researchers and Translucent, Inc., a technology leader in gallium nitride, will help graduate students appreciate the factors involved in developing a viable new technology. As well, the researchers are engaging in an outreach program (called "Alice in Wonderland") that is aimed at attracting female high-school students to the physical sciences and engineering. These students and physics instructors in local high schools are spending their summers at the University of Texas at Austin participating in research within a supportive environment.TECHNICAL DETAILS: The overarching objectives of this research project are to discover, understand and describe processes that lead to the formation of crystalline lanthanum, gadolinium, and erbium oxides on wurtzitic gallium nitride, GaN (0001). This research advances methods for precise interface engineering and elucidates the role of intermetallic compounds (called "Zintl compounds"), comprised of Group 1or 2 elements and Group 13-15 elements, in altering the surface energy to facilitate wetting and direct the [111] growth direction of the oxides on GaN (0001). The research benefits from the infrastructure, adjacency of related research, and expertise and complementary skills the academic researchers and the industrial partner bring in atomically controlled growth, materials characterization, surface chemistry, first-principles modeling and electrical characterization. Specific focus areas for the fundamental studies include: 1) discovery of approaches to grow crystalline, C-type La, Gd and Er oxide films epitaxially on GaN(0001) surfaces; 2) elucidation of the underlying interface chemistry responsible for oxide on semiconductor heteroepitaxy; and 3) exploring the structure-property-growth relationships so the results can be extended to additional oxide-semiconductor systems. The research uses molecular beam epitaxy and atomic layer deposition techniques to grow the epitaxial structures; first-principles density functional theory (DFT) approaches to identify suitable intermetallic compounds and to model the atomic structure, electric and electronic properties of the oxide-gallium nitride interface; and ex situ transmission electron microscopy (TEM) and electrical measurements to validate model predictions and establish structure-property relations.