Investigating the strain-tunable properties of ScAlN through first-principles calculations

Though ScAlN exhibits ferroelectricity due to the incorporation of ScN and its layered hexagonal phase, the strain on the wurtzite basal plane due to alloying or epitaxy also contributes to the ability of this material to exhibit polarization switching without reaching its dielectric breakdown limit. Since the applied field that allows for polarization switching is smaller than the dielectric strength of ScAlN, understanding the strain-tunable properties of the alloy is critical to obtaining a method to lower the energy barrier for ferroelectric switching. In this work, we investigate how increasing the strain of ScAlN through the incorporation of indium or by epitaxial lattice mismatch affects its dielectric permittivity and polarization switching energy barrier. We utilized density functional perturbation theory (DFPT) phonon calculations at the Brillouin zone center to determine the electronic and ionic contribution to the dielectric constant and performed nudged elastic band (NEB) calculations to quantify the effects of In composition on the polarization switching barrier of the alloy system. This work on the strain-tunable properties of ScAlN can be generalized to other III-nitride alloys like ScAlGaN and provides insight into the polarization switching mechanism of these systems.