Abstract
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 thanc-plane GaN. After indentation, lateral cracks emerge on the nonpolar GaN surface and preferentially propagate parallel to the 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 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.
Highlights
GaN-related III-nitride materials have drawn much attention over the last decade owing to its highly expected potential in short-wavelength optoelectronic devices, optical detectors, and semiconductor lasers [1, 2]
In order to further improve the performance of these devices, besides the optical and electrical properties of materials, mechanical characteristics and deformation behavior are crucial for solving the problems of residual stress/strain introduced by heteroepitaxial films and multiple-layer device structures
We investigate the main deformation features of nonpolar m-plane GaN thick films during nanoindentation
Summary
GaN-related III-nitride materials have drawn much attention over the last decade owing to its highly expected potential in short-wavelength optoelectronic devices, optical detectors, and semiconductor lasers [1, 2]. We investigate the main deformation features of nonpolar m-plane GaN thick films during nanoindentation. It has previously been reported that there are no cracks formed for loads up to as high as 900 mN with spherical indenter for c-plane hexagonal GaN [17].
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