Transmission electron microscopic investigations were made of defect structures in GaN/Al2O3(00•1) epilayers which had been grown by means of metal-organic chemical vapor deposition involving a 2-step process. The defect structures, which included threading dislocations, partial dislocations which bounded stacking faults, and inversion domains, were analyzed by using diffraction contrast, high-resolution imaging and convergent-beam diffraction techniques. The GaN film growth was initiated at 600C, with a nominal 20nm nucleation layer. This was followed by high-temperature growth at 1080C. The near-interfacial region of the films consisted of a mixture of cubic and hexagonal GaN which was characterized by the presence of a high density of stacking faults that were bounded by Shockley and Frank partial dislocations. The near-interfacial region contained a high density of inversion domains. When more than about 0.5 in thickness, the film consisted of isolated threading dislocations of either pure edge, mixed, or pure screw character; with a total density of about 7 x 108/cm2. The threading dislocation reduction in these films was associated with a cubic-to-hexagonal transformation of the nucleation layer region during high-temperature growth.

X.H.Wu, L.M.Brown, D.Kapolnek, S.Keller, B.Keller, S.P.DenBaars, J.S.Speck: Journal of Applied Physics, 1996, 80[6], 3228-37