Anisotropic intrinsic and extrinsic stresses in epitaxial wurtzitic GaN thin film on γ-LiAlO2 (1 0 0)

A wurtzitic GaN thin film with a thickness of 130 nm is heteroepitaxially deposited on γ-LiAlO2(1 0 0) substrate by ion-beam-assisted molecular beam epitaxy (IBA-MBE). Structural properties of the film are characterized by high-temperature X-ray diffraction in the temperature range of 25-600 °C. The experimental approach demonstrates a possibility to determine residual stresses in anisotropic epitaxial thin film at high temperature using diffraction. The mechanical and thermal behavior of the film is influenced by the anisotropic nature of GaN (11¯00) crystallographic plane oriented parallel to the substrate surface. The diffraction measurements show that the specific mismatch of the in-plane thermal expansion coefficients result in anisotropic compressive in-plane residual stresses in the film, with the stress in the a-direction significantly larger than in the c-direction over the whole temperature range. Moreover, since no signs of plastic deformation are detected, the temperature dependence of residual stresses allows to extrapolate intrinsic stresses formed in the film during the deposition.