Thick hydride vapour phase epitaxial GaN layers grown on sapphire with different buffers

We report a comparative study of the crystalline quality of thick GaN layer s grown by hydride vapour phase epitaxy, using a nitridation and a GaCl pre treatment of the sapphire as well as a reactive sputtered AlN buffer and me talorganic chemical vapour deposition grown GaN 'template' layers. The stru cture quality was investigated using X-ray diffraction measurement and cath odoluminescence spectroscopy and imaging of cross-section of the films. The morphology of the layers was revealed by optical and atomic force microsco py. A distinct reduction of both the columnar near-interface region and the domain formation were observed in layers grown on AIN and GaN 'template' b uffers resulting in improved bulk quality and significant smoother film sur faces.