Effect of additional hydrochloric acid flow on the growth of non-polar a-plane GaN layers on r-plane sapphire by hydride vapor-phase epitaxy

The effect of additional HCl flow on the growth of a-plane GaN layers on r-plane sapphire by hydride vapor-phase epitaxy was investigated. Upon increasing the additional HCl flow rate, the surface roughness of the a-plane GaN layers, as measured by atomic force microscopy, reduced. The crystal quality of a-plane GaN, however, deteriorated, as confirmed by high stacking fault density observed by transmission electron microscopy, relating to the increased nuclei density and mosaicity and a high full width at half maximum in the ω-scan X-ray rocking curve. These observations were attributed to the large difference of growth rate and etch rate along c-direction, and m-direction of a-plane GaN, which were originated from the surface energetics of the crystallographic planes of GaN.