A 240-nm thick Al_(0.4)In_(0.02)Ga_(0.58)N layer is grown by metal organic chemical vapour deposition,with an over 1-μm thick GaN layer used as a buffer layer on a substrate of sapphire(0001).Rutherford backscattering and channeling are used to characterize the microstructure of AlInGaN.The results show a good crystalline quality of AlInGaN(x_(min)= 1.5%) with GaN buffer layer.The channeling angular scan around an off-normal(1213) axis in the {1010} plane of the AlInGaN layer is used to determine tetragonal distortion e_T,which is caused by the elastic strain in the AlInGaN.The resulting AlInGaN is subjected to an elastic strain at interfacial layer,and the strain decreases gradually towards the near-surface layer.It is expected that an epitaxial AlInGaN thin film with a thickness of 850 nm will be fully relaxed (e_T=0). A 240-nm thick Al 0.4 (0.4) In 0.02 Ga 0.58 is grown by metal organic chemical vapor deposition with an over 1-μm thick GaN layer used as a buffer layer on a substrate of sapphire (0001) . Rutherford backscattering and channeling are used to characterize the microstructure of AlInGaN. The results show a good crystalline quality of AlInGaN (x min = 1.5%) with GaN buffer layer. The channeling angular scan around an off-normal (1213) axis in the {1010} plane of the AlInGaN layer is used to determine tetragonal distortion e_T, which is caused by the elastic strain in the AlInGaN. The resulting AlInGaN is subjected to an elastic strain at interfacial layer, and the strain decreases toward the near -surface layer. It is expected that an epitaxial AlInGaN thin film with a thickness of 850 nm will be fully relaxed (e_T = 0).