Strain Distributions in Non-Polar a-Plane In_xGa_1?xN Epitaxial Layers on r-Plane Sapphire Extracted from X-Ray Diffraction

By using x-ray diffraction analysis, we investigate the major structural parameters such as strain state and crystal quality of non-polar a-plane In_xGa_1?xN thin films grown on r-sapphire substrates by metalorganic chemical vapour deposition. The results of the inplane grazing incidence diffraction technique are analyzed and compared with a complementary out-of-plane high resolution x-ray diffraction technique. When the indium composition is low, the a-plane In_xGa_1?xN layer is tensile strain in the growth direction (a-axis) and compressive strain in the two in-plane directions (m-axis and c-axis). The strain status becomes contrary when the indium composition is high. The stress in the m-axis direction σ_yy is larger than that in the c-axis direction σ_zz. Furthermore, strain in the two in-plane directions decrease and the crystal quality becomes better with the growing of the In_xGa_1?xN film.