The surface morphology and atomic structure of InN grown on the Ga-rich GaN(00•1)-pseudo (1 x 1) structure was studied by scanning tunnelling microscopy. Spirals were formed as a result of screw dislocations emerging at the surface to relieve the strain from the lattice mismatch. Two additional types of strain relaxation mechanisms were also found, both due to the incorporation of excess Ga atoms from the starting pseudo (1 x 1) surface into the growing films. For films below 8nm where the Ga concentration was larger than 7%, the formation of stacking faults at the InN/GaN interface produced a triangular network on the surface. The density of the stacking faults was found to decrease with film thickness and with the gradual consumption of the Ga atoms, and the network was therefore no longer observable above a critical thickness that varies from 8 to 10nm. Instead, vacancy islands, one atomic layer deep, were formed to relieve the stain near the surface region. These results provided atomic scale insights into the interplay between the surface morphology and strain relaxation during the epitaxial growth of highly lattice mismatched InN/GaN heterostructures.

Spiral Growth and Formation of Stacking Faults and Vacancy Islands during Molecular Beam Epitaxy of InN on GaN(0001). Y.Liu, L.Li: Nanotechnology, 2011, 22[42], 425707