The growth of Al0.45Ga0.55N layers of 5 mu m thickness on planar and trench patterned (0001) sapphire substrates by hydride vapour phase epitaxy (HVPE) is investigated. The introduction of an AlN buffer layer prior to the planar growth of the Al0.45Ga0.55N layer led to improved structural properties as revealed by x-ray rocking curves. However, the addition of the AlN buffer layers was found to result in clusters of non c-oriented crystallites at the growth surface most probably due to crack formation in the AlN. Using stripe patterned sapphire substrates targeting reduction of strain, AlN buffer layers are found to promote the c-plane growth on the ridges. The total pressure was found to be an important growth parameter to favour c-plane layer growth on the ridges over formation of semipolar (11-22) AlxGa1-xN crystallites on the m-plane sidewalls of the trenches. The optimised ELO Al0.45Ga0.55N layers exhibit an enhanced surface morphology with neither cracking nor polycrystalline distortions and FVVHM of x-ray rocking curves of 1450" for the 002 reflection and 2030" for the 302 reflection. (C) 2012 Elsevier B.V. All rights reserved.