GaN films have been grown on SiC substrates with an AlN nucleation layer by using a metal organic chemical vapor deposition technique. Micro-cracking of the GaN films has been observed in some of the grown samples. In order to investigate the micro-cracking and microstructure, the samples have been studied using various characterization techniques such as optical microscopy, atomic force microscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy (TEM). The surface morphology of the AlN nucleation layer is related to the stress evolution in subsequent overgrown GaN epilayers. It is determined via TEM evidence that, if the AlN nucleation layer has a rough surface morphology, this leads to tensile stresses in the GaN films, which finally results in cracking. Raman spectroscopy results also suggest this, by showing the existence of considerable tensile residual stress in the AlN nucleation layer. Based on these various observations and results, conclusions or propositions relating to the microstructure are presented.

中文翻译：

---

在 SiC 上生长的 GaN 的微观结构表征

GaN 薄膜已经通过使用金属有机化学气相沉积技术在具有 AlN 成核层的 SiC 衬底上生长。在一些生长的样品中观察到了 GaN 薄膜的微裂纹。为了研究微裂纹和微观结构，已经使用各种表征技术对样品进行了研究，例如光学显微镜、原子力显微镜、拉曼光谱、扫描电子显微镜和透射电子显微镜 (TEM)。AlN 成核层的表面形态与随后过度生长的 GaN 外延层中的应力演变有关。通过 TEM 证据确定，如果 AlN 成核层具有粗糙的表面形态，这会导致 GaN 薄膜中出现拉应力，最终导致开裂。拉曼光谱结果也表明了这一点，通过显示在 AlN 成核层中存在相当大的拉伸残余应力。基于这些不同的观察和结果，提出了与微观结构有关的结论或命题。