Collaborative Research: Analysis of Defects and Their Causes in Bulk Aluminum Nitride Crystals

本项目旨在更好地理解和控制与升华产生的大块氮化铝晶体生长机制相关的缺陷。缺陷，如位错、层错、晶界、多型和反转域，将与晶体中的杂质、生长条件、热应力和机械应力相关。缺陷的类型、密度和空间分布将通过x射线形貌、透射电子显微镜、缺陷选择性蚀刻和装饰性氧化来测量。将确定由氧和碳引起的特定类型的缺陷。这些杂质通常以相对较高的浓度（~1019 cm-3）存在于氮化铝晶体中，因为它们在原始源氮化铝粉末、石墨加热元件和炉固定装置中浓度很高。这些元素引起堆积错误、沉淀和其他缺陷的倾向将通过比较具有广泛杂质浓度范围的晶体来研究。由于晶体取向和极性的差异也将被确定。温度和氮压力对晶体各向异性生长速率和随后出现的缺陷的影响将得到解决。将检查在不同温度和氮压力下产生的一系列晶体，以确定存在哪些缺陷，以及它们对表面步骤的影响。样品安装和其他物理约束对应力和随后的空间缺陷分布的影响将被检查。将测量晶体中的残余应力并建立模型。还将测量由抛光AlN晶体的机械作用引起的表面和亚表面损伤。从这些关于氮化铝缺陷的信息中得到的反馈，有望使晶体生长过程以一种有知识的方式进行修改，从而提高晶体质量。该项目涉及与电子/光子材料相关的基础研究问题，具有技术相关性，并将研究和教育活动相结合。该项目为研究生提供了学习晶体生长和缺陷表征的基本方面的独特机会。通过已建立的合作，学生将能够比单独调查更深入地研究研究问题。学生将参观国家实验室，获得使用最先进设备的宝贵经验，并与经验丰富的科学家互动。研究结果将通过在高质量的科学期刊上发表和组织一次材料研究学会专题讨论会广泛传播。学生将积极参与，在专业协会会议上展示他们的发现。研讨会将为女性和代表性不足的高中学生安排，以了解AlN晶体的生长和特性。首席研究员和他们的学生还将访问初中和高中讨论这个项目，并特别鼓励妇女和少数民族学生加入理工科。＊＊＊

This project aims for greater understanding and control of defects associated with growth mechanisms of bulk aluminum nitride crystals produced by sublimation. Defects such as dislocations, stacking faults, grain boundaries, polytypoids and inversion domains will be correlated to impurities in crystals, growth conditions, and thermal and mechanical stresses. The types, densities, and the spatial distribution of defects will be measured by x-ray topography, transmission electron microscopy, defect selective etching, and decorative oxidation. Specific types of defects caused by oxygen and carbon will be determined. These impurities are typically present at relatively high concentrations (~1019 cm-3) in AlN crystals as a result of their high concentrations in the original source AlN powder, graphite heating elements, and furnace fixtures. The tendency for these elements to cause stacking faults, precipitates, and other defects will be investigated by comparing crystals with a broad range of impurity concentrations. Differences due to the crystal orientation and polarity will also be determined. The impact of temperature and nitrogen pressure on anisotropic growth rates and defects subsequently present in the crystals will be resolved. A series of crystals produced at different temperatures and nitrogen pressures will be examined to determine which defects are present, and their resulting influence on surface steps. Effects of sample mounting and other physical constraints on stress and subsequent spatial defect distribution will be examined. Residual stress in crystals will be measured and modeled. Surface and subsurface damage caused by mechanical action of polishing the AlN crystals will also be measured. Feedback from this information on defects in AlN is expected to allow the crystal growth process to be modified in a knowledgeable way so that crystal quality can be improved. %%% The project addresses fundamental research issues associated with electronic/photonic materials having technological relevance, and integrates research and educational activities. The project provides graduate students with unique opportunities to learn fundamental aspects of crystal growth and defect characterization. Through the established collaborations, students will be able to study research issues in greater depth than would be possible under separate investigations. Students will visit national laboratories, gain valuable experience working with state-of-the-art equipment and interacting with experienced scientists. The results of the research will be broadly disseminated by publication in high quality scientific journals and by organizing a materials research society symposium. Students will be actively involved by presenting their findings at professional society meetings. Workshops will be arranged for women and under represented group high school students to learn about AlN crystal growth and characterization. Principal investigators and their students will also visit middle school and high school to discuss this project, and to provide special encouragement to women and minority students to join science and engineering. ***