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采用有机金属化学气相沉积设备用两步生长法在(0001)蓝宝石衬底上制备AlN薄膜。研究了预通三甲基铝(TMAl)使衬底铝化对外延AlN的影响。利用高分辨X射线衍射(XRD)技术和扫描电子显微镜(SEM)分析了样品的结晶质量以及外延膜中的残余应力。通过SEM观察发现,短时间的预通TMAl处理对AlN薄膜表面的影响不大;但随着预通时间的增加,表面会出现六角形的岛。通过优化TMAl的预通时间可以保护衬底被氮化有利于Al极性面AlN的生长,从而得到的Al极性面AlN表面比较平整;但是预通TMAl时间过长会使衬底表面沉积金属态铝而不容易形成平整的表面。X射线双晶摇摆曲线结果表明:样品的(0002)和(1012)面的X射线双晶摇摆曲线的半峰宽随着预通TMAl时间的不断增加,由此得出薄膜的晶体质量不断下降。这可以解释为:预通TMAl使形成的晶核不再规则,从而在成核层形成了很多亚颗粒降低了晶体质量。进一步对XRD结果分析,我们也发现了这样的应力变化。这种应力的变化起源可以归结于内应力(岛的合并在其晶界引入的应力)与外应力(晶格失配与热失配引起的应力)共同作用的结果。
AlN films were prepared on (0001) sapphire substrates by a two-step growth method using an organometallic chemical vapor deposition apparatus. The effect of aluminum on the epitaxial AlN by the pretreatment of trimethylaluminum (TMAl) was investigated. The crystal quality and the residual stress in the epitaxial film were analyzed by high resolution X-ray diffraction (XRD) and scanning electron microscopy (SEM). SEM observation shows that the short-time pre-TMAl treatment has little effect on the surface of AlN films, but hexagonal islands appear on the surface with the increase of pre-conduction time. By optimizing the TMAl pre-pass time can protect the substrate is nitrided in favor of the Al-polar AlN growth, resulting in Al-polar AlN surface is relatively flat; but pre-TMAl time will make the substrate surface deposition of metal State aluminum and not easy to form a flat surface. The results of X-ray double-crystal rocking curve show that the half-width of X-ray double crystal rocking curve of samples (0002) and (1012) increases with the increase of pre-TMAl time, . This can be explained as: pre-TMAl formed nuclei no longer rules, thus forming a lot of nucleation layer sub-particles reduce the crystal quality. Further analysis of XRD results, we also found that such stress changes. The origin of this stress variation can be attributed to the combined effect of internal stress (stress introduced by the island’s consolidation at its grain boundaries) and external stress (stress induced by lattice mismatch and thermal mismatch).