Chemical Routes to the Growth of Crystalline Functional Oxides on Germanium

在亚10纳米时代，半导体行业将面临新的挑战，因为缩放将不再是电子器件性能提升的主导。新材料和材料组合提供了一个机会，以最小的改变设备结构，提高性能和功能。例如，使用锗作为衬底可以提供更低的功耗和更快的计算速度。而利用兼具磁性和电子性的钙钛矿氧化物作为功能层，可以实现先进的存储器件、集成光隔离器和自旋电子器件。该研究将探索如何直接在锗上生长这些晶体钙钛矿氧化物薄膜。该研究探索了一种全化学生长过程，该过程应该是可扩展的，从制造成本上来说成本更低，并且基于当前的制造设备。其影响将体现在使未来的设备能够利用电荷和自旋的过程中。此外，研究人员还参与了一个名为“爱丽丝梦游仙境”的推广项目，旨在吸引女高中生学习物理科学和工程。这些来自当地高中的学生将在德克萨斯大学奥斯汀分校度过暑假，在一个支持性的环境中参与研究。本研究的首要目标是理解和描述在可扩展和可制造的化学沉积过程中导致在Ge（001）上形成具有必要铁电性和铁磁性的晶体多铁氧化物的过程。该研究探索了铁掺杂的钛酸钡，铁含量高达20%，以及直接在锗上生长的铋铁氧体晶体氧化物。本研究采用分子束外延法制备良好定义的表面和原子层沉积法制备外延结构；利用原位电子和光子光谱对薄膜和界面进行了表征；并通过非原位透射电镜、x射线散射、磁和电测量建立了结构-性能关系。这项研究得益于基础设施、相关研究的邻近和首席研究员带来的原子控制生长、材料表征、表面化学和电性能测量方面的专业知识。基础研究的具体重点领域包括：1)阐明形成结晶氧化物的Ge（001）氧化物界面的反应和结构变化；2)了解钙钛矿层中导致结晶膜的结构演变以及结构如何依赖于工艺条件；3)在多铁氧化物的背景下建立结构-性能-功能关系，该多铁氧化物在技术相关的温度窗内具有铁电性和铁/反铁磁性。

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.