Ferroelectric nitrogen-polar ScAlN heterostructures on 4H-SiC enabled by thin AlN buffer layers

The expansive functional landscape of ferroelectric nitrides has sharpened interest in host platforms that can preserve excellent structural quality while extending operation to high-temperature, harsh-environment regimes. 4H-SiC is especially compelling owing to its thermal robustness, high thermal conductivity, and close lattice correspondence with AlN. Here, we report robust ferroelectric ScAlN-on-4H-SiC heterostructures enabled by thin, exceptionally high-quality AlN templating, grown via plasma-assisted molecular beam epitaxy. A 40 nm nitrogen-polar AlN buffer layer on carbon-terminated 4H-SiC yields highly ordered and dense films, providing an abrupt, structurally coherent, true wurtzite interface for ScAlN heteroepitaxy. Across a broad Sc composition range, a single dominant epitaxial orientation and monocrystalline wurtzite character are maintained without detectable secondary phases. Electrical measurements reveal room-temperature ferroelectricity in as-grown films with coercive fields and remanent polarizations comparable to ScAlN films grown directly on conductive substrates. Taken altogether, these findings establish AlN templating on 4H-SiC as a practical route to structurally controllable and reproducible all-epitaxial ferroelectric nitride heterostructures for extreme-environment electronic, acoustic, and memory applications.