Verification of the hypothesis on the thermoelastic nature of deformation of $a$(0001)GaN layer grown on the sapphire $a$-cut

The deformation of $a$(0001)GaN epitaxial layer on the (11$\bar2$0) sapphire $a$-cut is studied by X-ray diffractometry. Anisotropic-layer deformation is calculated by reference data on the thermal expansion coefficients of gallium nitride and sapphire. A comparison of the calculated and experimental deformation confirms the hypothesis on the thermoelastic character of GaN deformation on the sapphire $a$-cut. This result makes it possible, in particular, to assess theoretically the elastic deformation and piezoelectric field in pseudomorphic heterostructures with GaN layers on the sapphire $a$-cut as a virtual substrate or a buffer layer.