Elastic strain in InGaN and AlGaN layers

InGaN and AlGaN layers were grown on Al2O3 substrate by metalorganic chemical vapor deposition (MOCVD) with a GaN intermediate layer. The thickness and the composition of the layers, 270 nm In0.18Ga0.82N and 765 nm Al0.28Ga0.72N, were determined by Rutherford backscattering (RBS). The elastic strain of these layers was determined by X-ray diffraction combined with RBS/channeling. The results show that these layers are partially strained with a perpendicular strain e⊥=+0.21%, parallel strain e||=−0.53% for the InGaN layer and e⊥=−0.16%, e||=+0.39% for the AlGaN layer. The signs of e|| and e⊥ of AlGaN are opposite to those of InGaN, since the lattice mismatch between AlGaN and GaN is negative while the lattice mismatch between InGaN and GaN is positive.