Strain Distributions in Non-Polar a-Plane In_(x)Ga_(1−x)N 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_(x)𝑦Ga_(1−x)𝑦N 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_(x)𝑦Ga_(1−x)𝑦N layer is tensile strain in the growth direction(𝑏a-axis)and compressive strain in the two in-plane directions(𝑛a-axis and𝑑a-axis).The strain status becomes contrary when the indium composition is high.The stress in the𝑛a-axis direction𝜏σyy is larger than that in the a-axis directionσzz.Furthermore,strain in the two in-plane directions decrease and the crystal quality becomes better with the growing of the In_(x)Ga_(1−z)N film.