Strain in AlGaN layer studied by Rutherford backscattering/channeling and x-ray diffraction

An AlGaN layer with good crystalline quality (χmin=2.1%) was grown by metalorganic vapor phase epitaxy on a sapphire (0001) substrate using a GaN intermediate layer. The Al composition, which cannot be unambiguously determined by x-ray diffraction (XRD) or by photoluminescence, was determined by Rutherford backscattering (RBS). The perpendicular and parallel elastic strain of the Al0.28Ga0.72N layer, e⊥=−0.16% and e∥=+0.39%, respectively, were derived using XRD and RBS/channeling. The small ratio |e⊥/e∥|=0.41 indicates that the Al0.28Ga0.72N lattice is much stiffer in the c-axis direction than in the a-axis direction. A comparison of the strain data for GaN, InGaN, and AlGaN layers is presented.