Growth window and wurtzite phase stability of molecular-beam-epitaxial ScInN thin films with composition-dependent photoluminescence

We establish the growth window and wurtzite phase stability of plasma-assisted molecular-beam-epitaxial ScInN thin films over a broad composition range. Lower growth temperatures suppress rock salt phase formation and enable wurtzite ScInN without detectable rock salt contributions up to x(Sc) = 0.36. X-ray diffraction reveals systematic composition-dependent changes in phase formation and lattice parameters. We observe a pronounced anisotropic lattice evolution, with the in-plane lattice parameter a showing only a minor dependence on scandium content, whereas a decrease in the out-of-plane lattice parameter c is more pronounced. This trend is consistent with results from density functional theory calculations we performed using the SCAN functional, as well as Raman spectroscopy measurements showing a strong shift of the A1(LO) modes and a much smaller shift of the E2 mode. Photoluminescence is observed across the investigated alloy series, with the maximum emission shifting from 0.85 eV for InN to 2.07 eV for x(Sc) = 0.40. These results establish molecular-beam-epitaxial ScInN as an experimentally accessible alloy system with an extended wurtzite stability range, a composition-dependent optical response, and a nearly constant in-plane lattice parameter enabling heterostructure design with reduced lattice mismatch.