Characterization of tetragonal distortion in a thick Al_0.2Ga_0.8N epilayer with an AlN interlayer by Rutherford backscattering/channeling

An Al_0.2Ga_0.8N/AlN/Al_0.2Ga_0.8N heterostructure was grown by metalorganic chemical vapor deposition on a sapphire (0001) substrate with a thick (>1 μm) GaN intermediate layer. The Al composition was determined by Rutherford backscattering (RBS). Using the channeling scan around an off-normal 1213 axis in the (1010) plane of the Al_0.2Ga_0.8N layer, the tetragonal distortion e_T, which is caused by the elastic strain in the epilayer, is investigated. The results show that e_T in the high-quality Al_0.2Ga_0.8N layer is dramatically released by the AlN interlayer from 0.66% to 0.27%.