Structural and morphological characterization of GaN(0001) layers grown on SiC by maskless pendeo-epitaxy via X-ray Microdiffraction

Novel white beam X-ray microdiffraction (WBD) together with high resolution monochromatic X-ray diffraction (HRXRD) and finite element simulations have been used to determine the distribution of strain, dislocations, sub-boundaries and crystallographic wing tilt in uncoalesced and coalesced GaN layers grown by maskless pendeo-epitaxy. In traditional HRXRD the spot size of the X-ray beam is large ($\sim $0.5 mm), i.e. it gives information averaged over 40-50 of stripes. In contrast, advanced WBD provides very local information and enables us to follow the local orientation at different locations across the stripe. Stress relaxation in the GaN layers occurs in conventional and in pendeo-epitaxial films via the formation of additional misfit dislocations, domain boundaries, elastic strain and wing tilt. An important parameter was the width-to-height ratio of the etched columns of GaN from which the lateral growth of the wings occurred. The strain and tilt across the stripes increased with the width-to-height ratio. Sharp tilt boundaries were observed at the interfaces formed by the coalescence of two laterally growing wings. The wings tilted upward during cooling to room temperature for both the uncoalesced and the coalesced GaN layers