Anisotropic microstructure of hydrothermally-grown non-polar a-plane ZnO on a-plane GaN film

Abstract

Nonpolar a-plane ZnO (a-ZnO) films with good crystalline quality have been achieved by a hydrothermal growth method on nonpolar a-plane GaN (a-GaN) films without any nucleation steps. The X-ray diffraction θ–2θ scan of the a-ZnO film grown on a-GaN film showed that the film was uniformly a-plane 112¯0 oriented. The a-ZnO films exhibited anisotropic peak broadenings of the on-axis rocking curves with X-ray in-beam orientations. The full width at half maximum of the on-axis rocking curve of nonpolar a-ZnO film along the c-axis direction was measured to be 2092arcsec, which is almost two times larger than the one along the m-axis direction (1219arcsec). The Williamson–Hall plot analysis of the symmetric 112¯0 and 224¯0 Bragg reflections showed that the mosaic tilt values were 0.647° and 0.407° along the c-axis and m-axis directions, respectively. It clearly indicates that large mosaic tilt along the c-axis in a-ZnO film is mainly responsible for the anisotropic peak broadenings of the on-axis rocking curves with respect to X-ray in-beam orientations.