Defect structures in In x Ga 1-x N films grown on GaN/Al 2 O 3 (0001) epilayers by metal-organic chemical vapour deposition (MOCVD) were investigated by means of transmission electron microscopy. The effects of the different growth parameters on the structural properties of the samples were examined. Defects, including threading dislocations, partial dislocations and V-defects were analyzed by diffraction contrast analysis.ABSTRACT