X-ray diffraction study of strain and defect structure of nonpolar a-plane GaN-layers grown on r-plane sapphire

Structural state of nonpolar a-plane GaN layers grown by MOVPE on r-plane sapphire is investigated by X-ray diffraction method. Interplanar spacings were measured in three directions and corresponding strains were determined. A crystalline perfection was studied by measurement of diffraction peaks of θ- and θ–2θ-scanning in Bragg- and Laue-diffraction geometry. Their FWHM was analyzed by Williamson–Hall plots. Anisotropy of the elastic strains and the peak broadening was revealed. It is shown that a different broadening of diffraction pattern in two in-plane directions is not caused by mosaicity and can be explained by a specific distribution of dislocations.