Investigation of the anisotropy of the structural properties of GaN(0001) layers grown by MOVPE on $a$-plane (11$\bar2$0) sapphire

The structural properties of GaN(0001) heteroepitaxial layers grown by metalorganic vapor phase epitaxy (MOVPE) on $a$-plane (11$\bar2$0) sapphire substrates are investigated by X-ray diffractometry. Anisotropy of the rocking-curve width for the symmetric (0004) and asymmetric $\{11\bar24\}$ and $\{10\bar15\}$ reflections of gallium nitride upon rotation of the sample is observed. A comparison of the anisotropy of the rocking-curve width for (0001)GaN/(11$\bar2$0)Al$_{2}$O$_{3}$ layers with two different variants of in-plane orientation relationships suggests that the anisotropy of the structural properties is independent of the thermoelastic stress arising upon cooling the heterostructure.