Microstructural evolution of a-plane GaN grown on a-plane SiC by metalorganic chemical vapor deposition

This letter describes the relationship between the morphological evolution of heteroepitaxial a-plane GaN films and the formation of the extended defect structure. The initial a-plane GaN growth on a-plane SiC substrates (via a high temperature AlN buffer layer) follows a Volmer–Weber growth mode. Consequently, the coalescence of three-dimensional (3D) islands generates threading dislocations which dominate the nonpolar GaN film’s microstructure ${\text{(3×10}}^{10}\hspace{0.17em}{\mathrm{cm}}^{\text{−2}}\mathrm{).}$ Exposed nitrogen-face surfaces, identified using x-ray diffraction measurements and convergent beam electron diffraction analysis, are present throughout the 3D growth and are the likely source of basal plane faulting ${\text{(7×10}}^5\hspace{0.17em}{\mathrm{cm}}^{\text{−1}})$ within the film. Atomic force microscopy and scanning electron microscopy were used to image the morphological transition, which was correlated to changes in the a-GaN crystal tilt mosaic measured by x-ray rocking curves.