Control of phase purity in high scandium fraction heteroepitaxial ScAlN grown by molecular beam epitaxy

ScAlN is a promising material for applications spanning wide-bandwidth filters, high-electron-mobility transistors, and ferroelectric memory. We investigate conditions influencing wurtzite phase purity for heteroepitaxial ScAlN, and present methods to rapidly identify phase purity degradation. Even for N-rich samples, phase purity is sensitive to the III/V ratio near the N-rich to metal-rich transition. Epitaxial ScxAl1−xN samples can be grown at 700 °C with x = 0.06–0.22, although the phase purity degrades for x = 0.32. By reducing the substrate temperature to 390 °C, we demonstrate 200 nm Sc0.32Al0.68N heteroepitaxial films with a record low rocking curve full-width at half-maximum of 1840 arcsec.