Chemical Routes to the Growth of Crystalline Functional Oxides on Germanium

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The semiconductor industry faces new challenges in the sub-10 nanometer era as scaling will no longer dominate performance improvement for electronic devices. New materials and combinations of materials provide an opportunity to improve performance and function with minimal change to the device construction. For example, using germanium as the substrate can provide both lower power consumption and faster computing speeds. And using perovskite oxides that are both magnetic and electronic as the functional layer can enable advanced memory devices, integrated optical isolators and spintronic devices. The research will explore how to grow these crystalline perovskite oxide films directly on germanium. The research explores an all-chemical growth process that should be scalable, is inherently less costly from a manufacturing cost of ownership, and is based on current manufacturing equipment. The impact will be in processes to enable future devices that exploit charge and spin. As well, the researcher engages 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 from local high schools will spend their summers at the University of Texas at Austin participating in research within a supportive environment. The overarching objectives of this research are to understand and describe processes that lead to the formation of crystalline multiferroic oxides on Ge(001) with the requisite ferroelectric and ferromagnetic properties in a chemical deposition process that is scalable and manufacturable. The research explores iron-doped barium titantate, with iron levels up to 20 percent, and bismuth ferrite crystalline oxides grown directly on Ge. The research uses molecular beam epitaxy to prepare well-defined surfaces and atomic layer deposition to grow the epitaxial structures; in situ electron and photon spectroscopies are used to characterize the films and interfaces; and ex situ transmission electron microscopy, and x-ray scattering, magnetic and electrical measurements establish structure-property relations. The research benefits from the infrastructure, adjacency of related research and expertise the principal investigator brings in atomically controlled growth, materials characterization, surface chemistry, and electrical property measurement. Specific focus areas for the fundamental studies include: 1) elucidating the reactions and structural changes at the Ge(001) oxide interface that seed crystalline oxide formation; 2) understanding the evolution of structure in the perovskite layer leading to a crystalline film and how the structure depends on process conditions; and 3) establishing the structure-property-function relationships in the context of a multiferroic oxide that features ferroelectric and ferro-/antiferromagnetic properties within a temperature window that is technologically relevant.