本文在具有0.2°至1.0°斜切角的c面蓝宝石衬底上通过金属有机化合物化学气相沉积(MOCVD)生长了台阶聚束表面形貌AlN外延层, 并系统研究了高温退火过程中其表面形貌演化规律, 且基于第一性原理计算揭示了表面形貌演化背后的物理机制。研究发现, 随退火温度逐步升高, AlN外延层台阶边缘首先出现具有六方结构特征的热刻蚀凹坑, 随后在台面上形成边缘规则的多边形凹坑, 其主要原因是AlN表面台阶边缘处Al-N原子对脱附能量(10.72 eV)小于台面处Al-N原子对脱附能量(12.12 eV)。此外, 由于台阶宽度随斜切角增大而变窄, 台面处凹坑在扩张过程中易与台阶边缘处凹坑发生合并形成V形边缘, 斜切角越大台面上凹坑数量越少。本文阐明了不同斜切角蓝宝石衬底上生长的AlN在高温热退火过程中台阶聚束形貌演变机制, 为面内组分调制的AlGaN基高效深紫外LED提供基础。

In this article, an AlN epitaxial layer with a step bunching surface morphology was grown on 0.2° to 1.0° offcut angle c-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD), and the evolution regularity of the surface morphology during high-temperature annealing (HTA) was systematically studied. The underlying physical mechanisms were further uncovered through first-principles calculations. It is revealed that as the annealing temperature gradually increase, thermal etching pits with hexagonal structure characteristics first appear on step edges, and then polygonal pits with regular edges formed on the step terraces. The main reason is that the energy of Al-N pairs decomposed from AlN surface at the step-bunching edges (10.72 eV) is smaller than that of Al-N pairs decomposed from the step terraces (12.12 eV), which leads to the phenomenon that the morphology of step edges will change firstly during HTA. In addition, because the width of the step becomes narrower with the increase of the miscut angle, the pits of the step terraces tend to merge with the pits of the step edges during the expansion process to form a V-shaped edge, resulting in step terraces with large miscut angle hardly appearing pits. This study clarifies the evolution mechanism of step-bunching morphology of AlN grown on sapphire substrates with various offcut angles during high-temperature annealing, and provides theoretical support for the preparation of high-quality AlN templates. This template can be used for AlGaN in-plane composition modulation to obtain high-efficiency deep-ultraviolet light-emitting diodes (DUV-LEDs).