Mechanical Deformation Behavior of Nonpolar GaN Thick Films by Berkovich Nanoindentation

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 < 11 (2) over bar0 > 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 < 11 (2) over bar0 > 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.

National High Technology Program of China 2006AA03A143 National Natural Sciences Foundation of China 60806001 Knowledge Innovation Program of the Chinese Academy of Sciences ISCAS2008T03 This study was supported by the National High Technology Program of China under Grant No. 2006AA03A143, the National Natural Sciences Foundation of China under Grant No. 60806001, and the Knowledge Innovation Program of the Chinese Academy of Sciences under Grant No. ISCAS2008T03. We would also like to thank Professor Li Chen of Peking University for his assistance in the Cathodoluminescence experiments.