Analysis of the defect structure of epitaxial GaN

The type and density of threading dislocations in GaN epitaxial layers grow n on c-plane sapphire have been analyzed by using nondestructive high resol ution X-ray diffraction. The highly distorted GaN layers were described as mosaic crystals characterized by a mean tilt and twist angle between the mo saic blocks which are correlated with the densities of screw and edge type threading dislocations, respectively Triple axis rocking curves of (00l) re flections for varying l-indices were used to determine the tilt angle, whil e the twist was extrapolated from omega-scans for (hkl) Bragg reflections w ith h or k nonzero, measured in skew symmetric diffraction geometry. This d efect analysis was applied to selected GaN layers grown by molecular beam e pitaxy (MBE) and metalorganic chemical vapour deposition (MOCVD) revealing clear differences between both sample types.