The lattice orientation of epitaxial GaN films grown on r-plane sapphire substrates by atmospheric metalorganic vapor-phase epitaxy was investigated. It is generally known that nonpolar a-plane GaN layers are grown on r-plane sapphire substrates. However, high-resolution X-ray diffraction revealed the large misorientation of GaN grown on r-plane sapphire when the growth temperature was increased from I 100 degrees C to 1150 degrees C. The c-axis was oriented to 25 degrees from the surface normal toward the ((1) over bar 101)(Sapphire) orientation. In addition, the GaN grown at 1150 degrees C indicated crystal twinning. These results were attributed to the anisotropic strain that was enhanced by higher growth temperature. (c) 2006 Elsevier B.V. All rights reserved.