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 degrees C with x = 0.06-0.22, although the phase purity degrades for x = 0.32. By reducing the substrate temperature to 390 degrees C, we demonstrate 200 nm Sc0.32Al0.68N heteroepitaxial films with a record low rocking curve full-width at half-maximum of 1840 arcsec.