Liu Jianming, Liu Xianlin, Li Chengming, Wei Hongyuan, Guo Yan, Jiao Chunmei, Li Zhiwei, Xu Xiaoqing, Song Huaping, Yang Shaoyan, Zhu Qinsen, Wang Zhanguo, Yang Anli, Yang Tieying, Wang Huanhua
Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, P, O, Box 912, Beijing 100083, People's Republic of China.
Nanoscale Res Lett. 2011 Jan 12;6(1):69. doi: 10.1186/1556-276X-6-69.
Cracks appeared in GaN epitaxial layers which were grown by a novel method combining metal organic vapor-phase epitaxy (MOCVD) and hydride vapor-phase epitaxy (HVPE) in one chamber. The origin of cracks in a 22-μm thick GaN film was fully investigated by high-resolution X-ray diffraction (XRD), micro-Raman spectra, and scanning electron microscopy (SEM). Many cracks under the surface were first observed by SEM after etching for 10 min. By investigating the cross section of the sample with high-resolution micro-Raman spectra, the distribution of the stress along the depth was determined. From the interface of the film/substrate to the top surface of the film, several turnings were found. A large compressive stress existed at the interface. The stress went down as the detecting area was moved up from the interface to the overlayer, and it was maintained at a large value for a long depth area. Then it went down again, and it finally increased near the top surface. The cross-section of the film was observed after cleaving and etching for 2 min. It was found that the crystal quality of the healed part was nearly the same as the uncracked region. This indicated that cracking occurred in the growth, when the tensile stress accumulated and reached the critical value. Moreover, the cracks would heal because of high lateral growth rate.
通过在一个腔室内将金属有机气相外延（MOCVD）和氢化物气相外延（HVPE）相结合的新方法生长的氮化镓外延层中出现了裂纹。利用高分辨率X射线衍射（XRD）、显微拉曼光谱和扫描电子显微镜（SEM）对厚度为22μm的氮化镓薄膜中裂纹的起源进行了全面研究。蚀刻10分钟后，通过SEM首次观察到表面下的许多裂纹。通过用高分辨率显微拉曼光谱研究样品的横截面，确定了沿深度方向的应力分布。从薄膜/衬底的界面到薄膜的顶面，发现了几个转折点。在界面处存在较大的压应力。随着检测区域从界面向上移动到覆盖层，应力下降，并在较深的区域长时间保持在较大值。然后应力再次下降，最终在靠近顶面处增加。在劈开并蚀刻2分钟后观察薄膜的横截面。发现愈合部分的晶体质量与未开裂区域几乎相同。这表明在生长过程中，当拉应力积累并达到临界值时就会发生开裂。此外，由于较高的横向生长速率，裂纹会愈合。
