Influence of Solute Incorporation Mechanisms on the Properties of Highly Mismatched Alloys

非技术描述：高度不匹配合金是指含有原子尺寸差异很大的化学元素和吸引附近电子的能力不同的材料。当在合金中加入几个大小不同的原子时，它的电学和光学特性往往会发生巨大的变化。这项研究的目的是研究原子的局部环境对合金薄膜和多层结构的电子和光学性能的影响，并着眼于温度不敏感激光器、高选择性自旋阀和高效光伏的工程结构。该项目为研究生、本科生和高中生提供培训，使他们与来自世界各地几所大学和实验室的研究人员合作。获得的新知识通过出版物和演讲以及研究生和本科生课程的发展广泛传播。外联活动强调对妇女和代表性不足的少数民族的指导。技术描述：该项目的重点是对溶质结合机制及其对高度不匹配合金的电子态、输运和光电子性能的影响的基本理解。该项目的主要目标是开发一个预测框架，用于替代N和Bi原子以及N- as， N-N或N-Bi对随机和有序GaAs（BiN）合金薄膜和异质结构的性能的影响。采用等离子体辅助分子束外延技术在多种衬底上制备了GaAs（BiN）合金，然后采用外延后快速热退火程序。利用原位反射高能电子衍射、多光束光学应力传感和扫描隧道显微镜/光谱技术，实时监测了表面重构、表面应力和局部电子态之间的相互作用。合金的化学计量学和局部原子环境被检查使用原子探针层析和新颖的通道离子束分析。为了确定溶质掺入机制与电子态之间的关系，将实验输运和光谱数据与原子和密度泛函理论计算进行了比较。除了确定四元合金相对于砷化镓的波段偏移的成分依赖外，还使用扫描隧道光谱和时间分辨光致发光检查了嵌套与交错波段偏移的特征。密歇根大学的项目涉及与国家实验室和国际大学的科学家合作，为参与的学生提供广泛的机会。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical Description: Highly mismatched alloys are materials that contain chemical elements with very different atomic sizes and different ability to attract nearby electrons. When a few atoms with larger or smaller sizes are added to an alloy, its electrical and optical properties often change dramatically. The goal of this research is to examine the impact of the atoms' local surroundings on the electronic and optical properties of alloy films and multi-layer structures, with an eye towards engineering structures for temperature-insensitive lasers, high-selectivity spin valves, and high efficiency photovoltaics. The project provides training to graduate, undergraduate, and high school students, engaging them in collaborations with investigators from several universities and laboratories throughout the world. The new knowledge acquired is broadly disseminated through publications and presentations, and graduate and undergraduate curriculum development. Outreach activities emphasize the mentoring of women and underrepresented minorities. Technical Description: The project is focused on fundamental understanding of solute incorporation mechanisms and their influence on the electronic states, transport, and optoelectronic properties of highly mismatched alloys. The primary goal of the project is to develop a predictive framework for the influence of substitutional N and Bi atoms, as well as N-As, N-N, or N-Bi pairs, on the properties of both random and ordered GaAs(BiN) alloy films and heterostructures. The GaAs(BiN) alloys are prepared on a variety of substrates using plasma-assisted molecular-beam epitaxy, followed by post-epitaxy rapid-thermal annealing sequences. The interplay between surface reconstruction, surface stress and local electronic states is monitored in real-time using in-situ reflection high-energy electron diffraction, multi-beam optical stress sensing and scanning tunneling microscopy/spectroscopy. The alloy stoichiometry and local atomic environments are examined using atom-probe tomography and novel channeling ion beam analyses. To determine the correlations between solute incorporation mechanisms and electronic states, the experimental transport and spectroscopic data is compared with both atomistic and density-functional theory computations. In addition to determining the composition dependence of band offsets of quaternary alloys with respect to GaAs, signatures for nested versus staggered band offsets are examined using scanning tunneling spectroscopy and time-resolved photoluminescence. The project at the University of Michigan involves collaborations with scientists at national laboratories and international universities, providing broad range of opportunities for the participating students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.