Ab initio density-functional theory simulations of scandium and aluminum nitride (${\mathrm{Al}}_{1-x}{\mathrm{Sc}}_x\mathrm{N}$) alloys have been carried out to investigate the impact of alloy configuration on their piezoelectric activity. The $d_{33,f}$ piezoelectric strain coefficient has been calculated for six ordered III-V configurations for ${\mathrm{Al}}_{0.5}{\mathrm{Sc}}_{0.5}\mathrm{N}$ alloys—including chalcopyritelike and CuPt-like structures. It varies from 9.3 to $41.4\mathrm{pm}{\mathrm{V}}^{-1}$, while its value for a randomized configuration is 28.3 $\mathrm{pm}{\mathrm{V}}^{-1}$. The alloy configurations have an impact on the degree of competition between near-neighbor coordination of the parent compounds (AlN, ScN) which is known to be responsible for local structural instabilities. This in turn affects (i) the strain sensitivity along the $c$ axis of the wurtzite internal parameter $u$ for Al and Sc sites and (ii) the stiffness of the material, both identified as key contributors to $d_{33,f}$. These findings suggest that spontaneous ordering of the alloy during film deposition or post-treatments should be considered as a way to optimize the piezoelectric activity of ${\mathrm{Al}}_{1-x}{\mathrm{Sc}}_x\mathrm{N}$ alloys.

• Received 9 May 2017

DOI:https://doi.org/10.1103/PhysRevMaterials.1.055402