Stabilization of wurtzite Sc0.4Al0.6N in pseudomorphic epitaxial ScxAl1−xN/InyAl1−yN superlattices
Pseudomorphic stabilization in wurtzite ScxAl1−xN/AlN and ScxAl1−xN/InyAl1−yN superlattices (x = 0.2, 0.3, and 0.4; y = 0.2-0.72), grown by reactive magnetron sputter epitaxy was investigated. X-ray diffraction and transmission electron microscopy show that in ScxAl1−xN/AlN superlattices the compressive biaxial stresses due to positive lattice mismatch in Sc0.3Al0.7N and Sc0.4Al0.6N lead to the loss of epitaxy, although the structure remains layered. For the negative lattice mismatched In-rich ScxAl1−xN/InyAl1−yN superlattices, a tensile biaxial stress promotes the stabilization of wurtzite ScxAl1−xN even for the highest investigated concentration x = 0.4. Ab initio calculations with fixed in-plane lattice parameters show a reduction in mixing energy for wurtzite ScxAl1−xN under tensile stress when x ⩾ 0.375 and corroborate the experimental results.