Ⅲ族氮化物外延层中的缺陷

采用光荧光和阴极荧光方法 ,对 Ga N外延层中的黄色和蓝色发光进行测量分析 ;同时 ,采用原子力显微镜、扫描电镜及其能谱测量外延层中的缺陷。结果表明 ,黄色和蓝色发光与残留杂质有关。采用第一原理计算结果显示 ,残留 C、O杂质、本征缺陷等是黄色和蓝色的可能物理起源。采用原子力显微镜、扫描电镜、透射电镜及其能谱对 Ga N/Al Ga N异质结中的纳米管进行观测 ,了解了纳米管的形貌。结果表明 ,构成纳米管的小面可能是外延过程中表面吸附引起的 ;计算结果显示 ,纳米管形貌变化与 Ga N/Al Ga N界面处晶格失配应力有关。采用透射电镜观察外延层中沉积物及其周围位错的结构表明 ,沉积物附近应力的存在是位错产生的主要原因

Defects in Ⅲ Nitrides Epilayers

Blue and yellow luminescence bands in undoped GaN epilayers were investigated and related to main residual C and O impurities by photoluminescence, which are suggested to be attributable to the electron transitions from O N states to V Ga states and between the inner levels of the C N O N complex, respectively, according to ab initio local density functional calculations. Larger nanopipes in undoped GaN/AlGaN hetero epilayers were imaged as dodecagonal pyramidal indentations, using atomic force microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). The calculations show that the structure of GaN/AlGaN interface with about 60° rotation forms when GaN epilayer is subjected to more than 14% compressive strain. The results suggest that the dodecagonal nanopipes may result from the interface rotation due to the strain. Precipitates in undoped AlGaN are surrounded by glide dislocation loops and helical dislocations in bright field TEM images that may be caused by the misfit stresses around the precipitates.