Stabilization of wurtzite Sc_0.4Al_0.6N in pseudomorphic epitaxial Sc_xAl_1−xN/In_yAl_1−yN superlattices

Pseudomorphic stabilization in wurtzite Sc_xAl_1−xN/AlN and Sc_xAl_1−xN/In_yAl_1−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 Sc_xAl_1−xN/AlN superlattices the compressive biaxial stresses due to positive lattice mismatch in Sc_0.3Al_0.7N and Sc_0.4Al_0.6N lead to the loss of epitaxy, although the structure remains layered. For the negative lattice mismatched In-rich Sc_xAl_1−xN/In_yAl_1−yN superlattices, a tensile biaxial stress promotes the stabilization of wurtzite Sc_xAl_1−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 Sc_xAl_1−xN under tensile stress when x ⩾ 0.375 and corroborate the experimental results