Piezoelectric, dielectric, and nonlinear optical properties of AlScN

Novel materials with very large electro-optic (EO) coefficients are required for creating ultracompact broadband modulators and for quantum transduction. Inspired by the finding that AlN/ScN superlattices could lead to higher EO coefficients [Phys. Rev. Lett. 123, 096801 (2019)], we employ density functional theory to calculate EO coefficients of solid-solution AlScN alloys and heterostructures using the supercell method. We find enhanced r_33 coefficients with elevated Sc concentration in AlScN alloys. At large Sc concentrations we find a remarkable enhancement in structures that have a large number of Sc-Sc pairs in 3^rd-nearest-neighbor positions. We are able to attribute this to large S_3i values (i=1,2,3) in the compliance tensor. We also observe enhanced EO coefficients in nonpolar a-plane (AlN)m/(ScN)n superlattices where both clamped and piezoelectric contributions to EO coefficients are increased by up to a factor of 20. Our results should help the design of AlScN alloys and heterostructures to achieve enhanced nonlinear optical properties.