Strain-induced bent domains in ferroelectric nitrides

Ferroelectric nitrides have emerged as promising semiconductor materials for modern electronics. However, their domain structures and associated properties are basically unknown, despite their potential to result in optimized or new phenomena. Density functional theory calculations are performed to investigate the effect of epitaxial strain on multidomains of (Al, Sc)N nitride systems and to compare it with the monodomain case. The multidomain systems are predicted to have five strain-induced regions, to be denoted as Regions I to V, respectively. Each of these regions is associated with rather different values or behaviors of physical properties such as axial ratio, polarizations, internal parameters, bond lengths, etc. Of particular interest is the prediction of bent domains under compressive strain extending beyond $-5.5$%, which indicates that domain walls may play a key role in the mechanical failure properties of these systems. Interestingly, such bending induces the creation of a finite in-plane polarization (in addition to out-of-plane dipoles) due to geometric and symmetry considerations. Strikingly too, the bent domains have lower energy than the wurtzite monodomains and have atomically sharp boundaries. Our findings may pave the way for domain-wall engineering in ferroelectric nitrides.