利用EBSD技术研究异质外延GaN单晶的缺陷和应力

The advantaged wide band gap semiconductor GaN is the next generation basis materials for microelectronics and optoelectronics industry. However, because of the lack of single crystal substrates, the GaN crystals are usually grown on foreign substrates. In this condition, the large residual stress and defect density in GaN are harmful to performance of devices. It is the bottle neck for the development of GaN based devices. The formation mechanism and distribution of stress and defects in GaN crystals grown on foreign substrates are not understood fully because of the limitation of current characterization method. A novel characterization method is needed urgently to be established to overcome the limitation in high resolution and large area mapping of stress. This research project is supposed basing on the electron backscatter diffraction (EBSD) technology. The high stress sensitivity, fast mapping, high spatial resolution and precise crystallographic orientation identification of EBSD are beneficial to the characterization of crystal materials. A calculation method about crystal stress from EBSD crystallographic orientation result will be established. The distribution of stress in HVPE grown GaN crystals on different substrates is researched by this method. Meanwhile, the crystal structure of defects in GaN will be identified by EBSD. This research will discover the formation mechanism and distribution of stress and defects in GaN crystal. The crystal quality will be improved by the adjustment of growth conditions based on the research result of this supposed project.

以GaN为代表的第三代半导体材料具有多种优良特性，是未来微电子、光电子产业的核心支撑材料。但是由于缺乏同质衬底，异质外延生长的GaN晶体具有较高位错密度和较大应力，对器件性能有较大的负面影响，这成为制约GaN晶体应用的主要瓶颈。目前由于测试技术所限，对GaN晶体中残余应力及缺陷的分布规律、产生机理等研究尚不成熟，急需一种新的方法对应力和缺陷进行深入研究，突破现有技术分辨率低、无法大面积扫描的局限。本项目基于EBSD技术的应变敏感性强、适合大面积扫描、空间分辨率高和标定准确等特点，提出一种根据EBSD晶体取向数据定量分析单晶中应力的方法，并对多种衬底上HVPE生长GaN单晶应力、缺陷的分布规律和产生机理进行研究。根据EBSD得到的GaN单晶中应力、缺陷的产生及分布规律，结合晶体生长理论指导调控HVPE生长工艺，获得高质量GaN单晶。

以GaN为代表的第三代半导体材料具有多种优良特性，是未来微电子、光电子产业的核心支撑材料。但是由于缺乏同质衬底，异质外延生长的GaN晶体具有较高位错密度和较大应力，对器件性能有较大的负面影响，这成为制约GaN晶体应用的主要瓶颈。目前由于测试技术所限，对GaN晶体中残余应力及缺陷的分布规律、产生机理等研究尚不成熟，急需一种新的方法对应力和缺陷进行深入研究，突破现有技术分辨率低、无法大面积扫描的局限。本项目基于EBSD技术的应变敏感性强、适合大面积扫描、空间分辨率高和标定准确等特点，比较了SiC和蓝宝石衬底异质外延生GaN单晶的晶体学取向关系和应力分布的规律；建立了一种根据EBSD晶体取向数据定量分析单晶中应力的方法，并将其应用在蓝宝石衬底生长GaN单晶，掌握了应力分布规律；通过EBSD设计的新型两步腐蚀多孔衬底上HVPE生长GaN单晶中孔隙结构对生长单晶的影响规律，阐明了孔隙结构影响GaN单晶质量和应力的机理；使用EBSD技术研究蓝宝石衬底小角晶界对异质外延生长GaN单晶的影响进行了研究，发现蓝宝石衬底中的小角晶界对GaN单晶晶体取向的影响及其随生长厚度的变化规律。通过本项目研究，拓展了EBSD技术在宽禁带晶体材料异质外延中的应用，同时结合晶体生长理论指导调控HVPE生长工艺，获得高质量GaN单晶。