Morphological study of non-polar (11-20) GaN grown on r-plane (1-102) sapphire

In order to grow high quality non-polar GaN-based LED structures, it is important to understand the mechanism of GaN growth by MOVPE on r-plane (1-102) sapphire. In this work, (11-20) GaN epilayers have been characterised at three stages of growth using high resolution X-ray diffraction (HRXRD), transmission electron microscopy (TEM) and atomic force microscopy (AIM). following nucleation, 3D islands were grown, then the V/III ratio was lowered and the islands coalesced to form a smooth film. A series of symmetric, XRD omega-scans obtained at different azimuthal angles revealed an anisotropy in the layers with respect to the [1-100] and [0001] axes. AFM scans show that the islands are elongated along the [0001] axis. TEM has been used to analyse the layers further. A high density of stacking faults (5x10(5) cm(-1)) and threading dislocations (4x10(10) cm(-2)) was found in the film with 120 s high V/III growth followed by low V/III growth. Defects were found to run perpendicular and at similar to 60 degrees to or the sapphire interface in uncoalesced "island" samples.