Structural evolution in sputter-epitaxial ScAlN films on GaN/SiC substrates

Scandium aluminum nitride (ScxAl1−xN) is a promising ferroelectric material for next-generation devices owing to its high Curie temperature and large spontaneous polarization. However, increasing Sc content can degrade crystallinity, affecting device performance. In this study, we investigate the structural evolution of of ScxAl1−xN films (x = 0.13–0.38) grown by sputter epitaxy on GaN/6H-SiC substrates, focusing on the effects of Sc composition and growth temperature. Surface morphology, structure, and lattice constants were characterized by AFM, XRD, and RHEED. All films exhibited atomically flat surfaces. The wurtzite phase was retained at lower Sc contents up to 625 °C. At x ≥ 0.34, especially at 675 °C, rocksalt-phase domains and polycrystalline features appeared. The c-axis lattice constant decreased with increasing Sc content and further contracted at higher temperatures, indicating the onset of a structural transition. These results indicate that both composition and temperature significantly influence the structural evolution of ScxAl1−xN films. Our results demonstrate that sputter epitaxy enables the controlled incorporation of Sc while maintaining structural coherence at moderate Sc contents. The observed evolution in crystal phase, surface morphology, and lattice parameters provides critical insight into the growth dynamics of ScAlN films, offering guidance for future integration into ferroelectric nitride semiconductor devices.