Persistent photoconductivity in titanate semiconductor crystals

非技术性说明：该项目研究了一种新的现象，即最近在室温下观察到的持久光电导性。具有这种独特性质的样品在暴露于光时会经历电导率的急剧增加，这种电导率在光关闭后会持续很长时间。钛酸锶是一种透明晶体，在室温下表现出大的持久光电导性，为从光学存储设备到表面金属电镀的工业应用开辟了可能性。研究小组正试图描述导致这种不寻常行为的缺陷，最大限度地扩大影响范围，并在新材料中发现它。他们使用最先进的设备来生长新型晶体并研究其物理特性。参与这项研究的学生进行动手实验，在国际会议上展示结果，并与创业公司会面，讨论潜在的应用。结合研究的光学主题，课程开发为小学教育学生寻求中等科学证书的必修课程。这些关于波和光的课程针对的是由下一代科学标准和华盛顿州专业教育者标准委员会、中级科学认证竞争对手定义的K-12学习目标。技术描述：该项目旨在实现氧化物半导体中的大的、室温下的持久光电导性，并利用该现象来推进有关电子输运等基本过程的知识。动力学，能垒高度，和基本缺陷的性质进行了研究。这些研究也阐明了氧化物中与氢有关的络合物的结构。该研究小组正试图在钛酸钡中实现大的室温持久光电导性，钛酸钡是一种铁电材料，可以表现出比以前在钛酸锶中发现的更大的电导率变化。利用这种独特的现象来研究电性能，在一个明确定义的范围内的载流子浓度，以提供深入了解散射机制和小极化子与自由电子传输。利用华盛顿州立大学独特的设施，晶体生长具有高纯度和受控的缺陷数量。这些晶体包括被设计为具有最佳性能的固溶体（合金）。各种实验方法，包括霍尔效应、红外光谱和光致发光，被用来研究持续光电导性和负责它的缺陷。除了提供基本的见解，建立缺陷和输运性质是重要的，因为它将允许研究人员控制（即，诱导和擦除）并优化效果。这项研究所获得的基础知识可以为全息存储、光学定义电子学和选择性电镀提供基础。该奖项反映了NSF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。

Nontechnical description:The project investigates a novel phenomenon, persistent photoconductivity, which was recently observed at room temperature. Samples with this unique property experience a dramatic increase in electrical conductivity when exposed to light, which persists long after the light is turned off. Strontium titanate, a transparent crystal, exhibits large persistent photoconductivity at room temperature, opening possibilities for industrial applications ranging from optical memory devices to electroplating of metals on surfaces. The research team is attempting to characterize the defects that are responsible for this unusual behavior, maximize the size of the effect, and discover it in new materials. They use state-of-the-art facilities to grow novel crystals and study their physical properties. Students involved in this research perform hands-on experiments, present results at international conferences, and meet with startup companies to discuss potential applications. In conjunction with the optical theme of the research, lessons are developed for a required course for elementary education students seeking the middle science credential. These lessons on waves and light target the K–12 learning goals defined by the Next Generation Science Standards and Washington State Professional Educator Standards Board, Middle Level Science Endorsement Competencies.Technical description:The project aims to achieve large, room-temperature persistent photoconductivity in oxide semiconductors and exploit the phenomenon to advance knowledge about fundamental processes such as electronic transport. Kinetics, energy-barrier heights, and fundamental defect properties are investigated. These studies also elucidate the structure of hydrogen-related complexes in oxides. The research team is attempting to achieve large, room temperature persistent photoconductivity in barium titanate, a ferroelectric material that could exhibit larger conductivity changes than those previously discovered in strontium titanate. This unique phenomenon is exploited to investigate electrical properties, over a well-defined range of carrier concentrations, to provide insight into scattering mechanisms and small-polaron versus free-electron transport. Using unique facilities at Washington State University, crystals are grown with high purity and controlled defect populations. These crystals include solid solutions (alloys) that are designed to have optimal properties. A variety of experimental methods, including Hall effect, infrared spectroscopy, and photoluminescence, are used to study the persistent photoconductivity and the defects responsible for it. Besides providing fundamental insight, establishing defect and transport properties is important because it will allow researchers to control (i.e., induce and erase) and optimize the effect. The fundamental knowledge gained in this study could provide the basis for holographic storage, optically defined electronics, and selective electroplating.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.