Nanoscale Res Lett. 2009 Jul;4(7):753-7. doi: 10.1007/s11671-009-9310-1. Epub 2009 Apr 25.
In this study, the deformation mechanisms of nonpolar GaN thick films grown on m-sapphire by hydride vapor phase epitaxy (HVPE) are investigated using nanoindentation with a Berkovich indenter, cathodoluminescence (CL), and Raman microscopy. Results show that nonpolar GaN is more susceptible to plastic deformation and has lower hardness than c-plane GaN. After indentation, lateral cracks emerge on the nonpolar GaN surface and preferentially propagate parallel to the ⟨112̄0⟩ orientation due to anisotropic defect-related stresses. Moreover, the quenching of CL luminescence can be observed to extend exclusively out from the center of the indentations along the ⟨112̄0⟩ orientation, a trend which is consistent with the evolution of cracks. The recrystallization process happens in the indented regions for the load of 500 mN. Raman area mapping indicates that the distribution of strain field coincides well with the profile of defect-expanded dark regions, while the enhanced compressive stress mainly concentrates in the facets of the indentation.
在这项研究中，使用压痕法（Berkovich 压头）、阴极发光（CL）和拉曼显微镜研究了在 m-蓝宝石上通过氢化物气相外延（HVPE）生长的非极性 GaN 厚膜的变形机制。结果表明，非极性 GaN 比 c 面 GaN 更容易发生塑性变形，硬度也更低。压痕后，非极性 GaN 表面出现横向裂纹，由于各向异性与缺陷相关的应力，这些裂纹优先沿 ⟨112̄0⟩方向平行扩展。此外，CL 发光的猝灭可以观察到仅从压痕中心沿 ⟨112̄0⟩方向向外扩展，这一趋势与裂纹的演化一致。在 500 mN 的载荷下，压痕区域发生再结晶过程。拉曼面积映射表明，应变场的分布与缺陷扩展暗区的轮廓很好地吻合，而增强的压应力主要集中在压痕的棱上。
