Coherent X-ray scattering phenomenon in highly disordered epitaxial AIN films

AIN films, grown by metalorganic chemical vapour deposition on c-plane sapphire, were investigated by high-resolution X-ray diffraction. In Ω-scans very narrow peaks superimposed on a broader signal were found. The occurrence of very narrow rocking curves is explained in terms of coherent X-ray scattering. This phenomenon is caused by a small rotational out-of-plane disorder in a resolution-limited component of the rocking curve. The tilt (out-of-plane disorder) of individual crystallites is caused by a rotation with small angles around an axis lying parallel to the surface. The diffuse component of the rocking curve was used for the structural characterization of the epitaxial films and a detailed determination of structural imperfection by X-ray diffraction could be obtained by measuring asymmetric reflections. The structural properties of the AIN films are confirmed by atomic force microscopy and transmission electron microscopy.