Layers were grown on c-plane sapphire substrates by metal-organic chemical vapour deposition with a conventional 2-step growth method. The effect of the 3-dimensional growth mode time (t3D), which depends on trimethylgallium flow rate and growth temperature, on the crystalline quality of the GaN layers was investigated by high resolution X-ray diffraction. Tilt and twist angles were estimated from full-width at half-maximum of the omega rocking curves (ω-RCs) recorded from the planes parallel and perpendicular to the sample surface. Grazing incidence X-ray diffraction was used for a direct measurement of the twist angle. The threading dislocation densities of GaN layers were estimated from the full-width at half-maximum values of (0002) and (10•0) ω-RCs. It was found that while the screw-type dislocations were independent of t3D, the edge-type dislocation density decreased with increasing t3D. Investigations of the structural defects using transmission electron microscopy showed that almost all dislocations generated during the growth of GaN were pure edge or mixed type.

Study of Defects Evolution in GaN Layers Grown by Metal-Organic Chemical Vapor Deposition. J.H.Jang, A.M.Herrero, B.Gila, C.Abernathy, V.Craciun: Journal of Applied Physics, 2008, 103[6], 063514