Determination of Alloy Composition and Residual Stress for AlxGa1-xN/GaN Epitaxial Films

The alloy composition and the residual stress in AlxGa1—xN on GaN epi-layers can be estimated by measuring both the a-axis and c-axis lattice constants using HRXRD. Using linear elastic theory, we derive the alloy composition of a biaxial strained layer from a simple equation relating the measured c-axis and a-axis lattice constants, the lattice constants for unstrained AlxGa1—xN (assuming Vegard's law), and the ratio of elastic stiffness constants. The method was used to calculate the composition and strain, as well as error estimates, for a set of AlxGa1—xN layers grown by MOCVD with 0.23 ≤ x ≤ 0.84.