New Methods for Defect Manipulation in Semiconducting Oxides

非技术描述固体的技术上有用的性质通常取决于它所含缺陷的类型和浓度。在氧化物半导体中，缺陷，如固体原子有序排列中的空位或嵌在结构中的额外原子，控制着某些催化剂用于环境修复的有效性，重要类型传感器的灵敏度，以及将太阳光转换为电能的设备的效率。目前用于控制缺陷行为的方法受到固体消耗、结构损伤或加入不想要的原子的影响。目前的研究试图开发基于对表面化学状态的控制或基于光照射的氧化物半导体中的全新缺陷操纵形式。这项工作采用了二氧化钛(一种具有重要技术价值的氧化物半导体)中扩散的实验测量，并建立了广泛的数学模型。这项研究与为高年级本科生和研究生开设的一门由行业支持的实验室课程“半导体材料合成中的化学与运输”同步进行。此外，正在根据学术文献对这一概念进行检验，即顾问-门徒关系在重要方面反映了亲子关系。最后，正在进行几项活动，以促进伦理在科学和工程中的重要性。技术检测缺陷处理依赖于三种最近发现的机制：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。表面与体缺陷的耦合通过静电和表面键插入/产生机制发生。缺陷迁移率和浓度的光学刺激是通过改变缺陷电荷状态来实现的。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产生和湮灭速率的可能性。量化是通过详细的连续模型完成的，并通过光学光反射对近表面电场进行表征。这项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模拟实验，量化了光刺激的效果。

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.