New Methods for Defect Manipulation in Semiconducting Oxides

非技术描述固体在技术上有用的特性通常取决于它所含缺陷的类型和浓度。在氧化物半导体中，诸如固体有序原子排列中的空位或楔入结构中的额外原子等缺陷控制着某些环境修复催化剂的有效性、重要类型传感器的灵敏度以及将阳光转换为电能的设备的效率。目前控制缺陷行为的方法受到固体消耗、结构损坏或不需要的原子的掺入的影响。目前的研究旨在开发基于表面化学状态控制或光照射的氧化物半导体中全新形式的缺陷操纵。这项工作采用二氧化钛（一种技术上重要的氧化物半导体）扩散的实验测量，并辅以广泛的数学模型。这项研究与一门为高年级本科生和研究生开设的实验室课程“半导体材料合成中的化学和输运”同时进行。此外，这一概念正在根据学术文献进行审查，即顾问与门徒的关系在重要方面反映了父母与子女的关系。最后，正在进行几项活动，以促进科学和工程伦理的重要性。技术细节缺陷操作依赖于最近发现的三种机制：两种用于体-表面耦合，一种用于缺陷形成和迁移的光学刺激。本体缺陷的表面耦合是通过静电和表面键插入/产生机制发生的。缺陷迁移率和浓度的光学刺激是通过缺陷电荷状态的变化来实现的。特别合成的二氧化钛结构提供了测量表面空位和间隙原子的生成和湮灭速率的可能性。量化是通过详细的连续体建模，通过光学光反射率表征近表面电场来完成的。研究考察了表面晶体取向、表面极性程度、气体吸附和掺杂水平的影响。通过在超带隙照明下进行的类似实验，量化了光刺激的影响。

NON-TECHNICAL DESCRIPTIONThe technologically useful properties of a solid often depend upon the types and concentrations of the defects it contains. In oxide semiconductors, defects such as vacancies in the ordered atomic arrangement of the solid or extra atoms wedged into the structure control the effectiveness of certain catalysts for environmental remediation, the sensitivity of important kinds of sensors, and the efficiency of devices for converting sunlight to electrical power. Current methods for controlling defect behavior suffer from consumption of the solid, structural damage, or incorporation of unwanted atoms. The present research seeks to develop entirely new forms of defect manipulation in oxide semiconductors based on control of the chemical state of the surface or on illumination by light. The work employs experimental measurements of diffusion in titanium dioxide (a technologically important oxide semiconductor) supported by extensive mathematical modeling. This research takes place in parallel with development of an industry-supported laboratory course for upper-division undergraduates and graduate students called "Chemistry and Transport in Semiconductor Materials Synthesis." In addition, the notion is being examined based on scholarly literature that the advisor-protege relationship mirrors the parent-offspring relationship in important respects. Finally, several activities to promote the importance of ethics in science and engineering are being pursued.TECHNICAL DETAILSThe defect manipulation relies upon three recently-discovered mechanisms: two for bulk-surface coupling and one for optical stimulation of defect formation and migration. Surface coupling to bulk defects occurs through electrostatic and surface bond insertion/generation mechanisms. Optical stimulation of defect mobilities and concentrations occurs through changes in defect charge state. Specially synthesized structures of titanium dioxide offer the possibility to measure generation and annihilation rates of vacancies and interstitial atoms at surfaces. Quantification is accomplished through detailed continuum modeling backed by characterization of near-surface electric fields through optical photoreflectance. The research examines the effects of surface crystallographic orientation, degree of surface polarity, gas adsorption, and doping level. The effects of optical stimulation are quantified by analogous experiments performed under super-bandgap illumination.