Due to the large misfits which were involved, nitride layers which were deposited onto (00•1) sapphire grew in a mosaic form. It was suggested that such a microstructure might not be due only to growth errors, as was usually argued. The threading dislocations, which were mainly of a-type, exhibited 5/7 and 8 atom ring cores. They formed sub-grain boundaries, and many of them were connected to 60º interface misfit dislocations. This was suggested to be an explanation for the rotation of individual islands around the c growth-axis.

The Structure of Threading Dislocations Generated at the GaN/Al2O3 Interface. P.Ruterana, V.Potin, G.Nouet: Materials Science Forum, 1999, 294-296, 349-52