Mosaic growth of GaN on (0001) sapphire: A high-resolution electron microscopy and crystallographic study of threading dislocations from low-angle to high-angle grain boundaries
Mosaic growth of GaN on (0001) sapphire: A high-resolution electron microscopy and crystallographic study of threading dislocations from low-angle to high-angle grain boundaries
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DOI：
10.1103/physrevb.61.5587
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发表时间：
2000-02
影响因子：
3.7
通讯作者：
V. Potin;P. Ruterana;G. Nouet;R. Pond;H. Morkoç
中科院分区：
文献类型：
--
作者：
V. Potin;P. Ruterana;G. Nouet;R. Pond;H. Morkoç
使用高分辨率电子显微镜、各向异性弹性计算和图像模拟，确定了通过分子束外延在蓝宝石上生长的 GaN 层中的纯边缘螺纹位错的典型对比度。人们发现它们的原子结构呈现出 5/7 或 8 个原子循环。对于孤立位错和小角度边界，以相似的频率观察到这两种配置。重合晶界已经被研究过，它们都是由具有上述确定的原子结构的纯刃位错组成。为了确定界面处的缺陷含量，对高角度边界进行了拓扑分析。因偏离重合而引入的缺陷与步骤相关，并且它们的伯格斯向量对应于位移位移完整集的最小向量。在界面处，发现出现了属于重合位点晶胞的侧面或对角线的无缺陷台阶。一些边界的重建只能通过考虑位错核心表现出 4 原子环循环的结构单元的出现来实现。在非对称界面中，发现一种由5/4/7原子环组成的新结构单元构成一个晶界位错的核心。
Using high-resolution electron microscopy, anisotropic elasticity calculations, and image simulations, typical contrast was identified for the pure edge threading dislocations in GaN layers grown by molecular-beam epitaxy on sapphire. Their atomic structure was found to exhibit 5/7, or 8 atom cycles. The two configurations were observed at a similar frequency for isolated dislocations and low-angle boundaries. Coincidence grain boundaries have been studied and they are all made of pure-edge dislocations with the above identified atomic structures. A topological analysis of high-angle boundaries has been carried out in order to determine the defect content at the interfaces. The defects introduced on deviation from coincidence are associated with steps and their Burgers vectors correspond to the smallest vectors of the displacement shift complete set. At the interfaces, defect free steps, which belong to the sides or diagonal of the coincident site lattice unit cell, have been found to occur. The reconstruction of some boundaries was only possible by taking into account the occurrence of structural units which exhibit 4-atom ring cycles for the dislocation cores. In nonsymmetric interfaces, a new structural unit made of 5/4/7 atom rings has been found to constitute the core of one grain boundary dislocation.