Analysis of the Defect Structure of Epitaxial GaN

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