Large misorientation of GaN films grown on r-plane sapphire substrates by metalorganic vapor-phase epitaxy

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 from1100 °C to 1150 °C. The c-axis was oriented to 25° from the surface normal toward the (1̄ 1 0 1)_Sapphire orientation. In addition, the GaN grown at 1150 °C indicated crystal twinning. These results were attributed to the anisotropic strain that was enhanced by higher growth temperature.