Determination of Composition and Lattice Relaxation in Semipolar Ternary (In,Al,Ga)N Strained Layers from Symmetric X-ray Diffraction Measurements

We present a new method to simultaneously determine the composition and strain state for thin (In,Al,Ga)N layers grown in semipolar orientations using the data from one symmetric on-axis reciprocal space map or four symmetric on-axis rocking curve X-ray measurements. The method makes use of the one-dimensional nature of lattice mismatch relaxation in semipolar III–nitride heterostructures via operation of a unique slip system, i.e., ( a /3) <1120> (0001) in the basal plane. The correlation between lattice tilt and misfit dislocation density is applied to determine the degree of relaxation, whereas the composition is found from the Bragg's law accounting for the change in planar spacing in elastically strained anisotropic wurzite (In,AlGa)N layers.