(1 1 (2) over bar 0) a-plane gallium nitride has been investigated by Raman spectroscopy and X-ray diffraction. Strains of a-plane GaN grown on LT-GaN nucleation layer were both compressive along [1 (1) over bar 0 0] and [0 0 0 2] orientations. However, strains of GaN epitaxied on HT-AlN buffer were tensile along [0 0 0 2] and compressive along [1 (1) over bar 0 0] GaN orientation. The crystalline anisotropy and quality were also improved by the HT-AlN layer. Atomic force microscopy was utilized for analyzing the HT-AlN buffer layer. We ascribed this divergence of strain and improvement of crystalline to the thermal expansion and lattice mismatch effects of HT-AlN buffer during the metalorganic vapor phase epitaxy. (C) 2012 Elsevier B.V. All rights reserved.