Properties of nonpolar a-plane GaN films grown by HVPE with AlN buffers

The influence of high temperature AlN buffer layers on the morphology, structural and optical characteristics of a-plane GaN grown by hydride vapour phase epitaxy on r-plane sapphire was investigated. While the morphology of the a-GaN was found to be significantly improved by using a-plane AlN buffer layer similarly to the effect observed in c-plane hydride vapour phase epitaxy GaN growth, the microstructure ensemble was revealed to be more complicated in comparison to that of the c-plane GaN. Higher dislocation density and prismatic stacking faults were observed. Moreover, in-plane anisotropic structural characteristics were revealed by high resolution X-ray diffraction employing azimuthal dependent and edge X-ray measurement symmetric geometry. In addition, the near band edge photoluminescence peaks, red-shifted with respect to that in c-plane GaN were observed. The latter were explained by the influence of the higher defect density and more complex strain distribution.