  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.
