Sapphire surface pits as sources of threading dislocations in hetero-epitaxial GaN layers

Sapphire substrates showed nanosized surface pits after the growth of GaN layers using a two-step process by hydride vapor-phase epitaxy. Threading dislocations with Burgers vectors of c and c + a were found to originate from the pits. Cross-sectional transmission electron microscopy observations are used to elucidate the mechanism of dislocation generation.