Abstract In this study, the effect of the annealing atmosphere (N2–CO and pure N2 atmosphere) on the crystal quality, surface morphology, and surface O content of the annealed AlN buffer layers was studied. The FWHM of the (0002) plane of an XRD rocking curve showed that the screw dislocation density of the as-grown AlN film can be reduced by annealing in both N2–CO and pure N2 atmosphere. The AlN film showed an improvement in crystal quality under pure N2 annealing atmosphere. As annealing the AlN buffer layer improves the crystal quality, surface roughness, and surface O content of the AlN film, it should be well controlled for the subsequent growth of III-nitride layers. The surface oxidation that occurred on the AlN films during annealing in N2–CO atmosphere resulted in an increase in surface O content and surface roughness of the AlN films, which is undesirable for the subsequent growth of III-nitride layers. We observed that the surface O content (in the depth of 2-nm) of all annealed AlN films was reduced in the N2 annealing atmosphere, which could be due to the O outgassing from the AlN surface to the pure N2 annealing atmosphere. The O outgassing of the surface O content in the AlN surface layer was related to the volume of space in the annealing setups. However, a large volume of annealing space under pure N2 gas flow resulted in higher thermal decomposition on the annealing AlN films, leading to pits forming on the annealed AlN surface and a smearing of the original step-terrace structure. Therefore, we found that there is an optimal annealing atmosphere space in maintaining the original surface morphology and achieving low surface O content in the annealed AlN film.

中文翻译：

---

退火气氛（CO和N2气流）对AlN缓冲层表面形貌和晶体质量的影响

摘要 在本研究中，研究了退火气氛（N2-CO 和纯 N2 气氛）对退火后的 AlN 缓冲层的晶体质量、表面形貌和表面 O 含量的影响。XRD 摇摆曲线的 (0002) 面的 FWHM 表明，通过在 N2-CO 和纯 N2 气氛中退火，可以降低生长的 AlN 膜的螺旋位错密度。AlN 薄膜在纯 N2 退火气氛下显示出晶体质量的改善。由于对 AlN 缓冲层进行退火可以改善 AlN 薄膜的晶体质量、表面粗糙度和表面 O 含量，因此应很好地控制后续 III 族氮化物层的生长。在 N2-CO 气氛中退火过程中 AlN 膜上发生的表面氧化导致 AlN 膜的表面 O 含量和表面粗糙度增加，这对于 III 族氮化物层的后续生长是不希望的。我们观察到所有退火的 AlN 薄膜的表面 O 含量（在 2 nm 的深度）在 N2 退火气氛中降低，这可能是由于 O 从 AlN 表面释放到纯 N2 退火气氛中所致。AlN 表面层中表面 O 含量的 O 释气与退火设置中的空间体积有关。然而，在纯 N2 气流下大量的退火空间导致退火 AlN 膜上的更高热分解，导致在退火的 AlN 表面形成凹坑，并涂抹原始的阶梯平台结构。因此，我们发现在保持原始表面形貌和实现退火 AlN 薄膜中低表面 O 含量方面存在最佳的退火气氛空间。