Towards higher electro-optic response in AlScN

Novel materials with large electro-optic (EO) coefficients are essential for developing ultra-compact broadband modulators and enabling effective quantum transduction. Compared to lithium niobate, the most widely used nonlinear optical material, wurtzite AlScN offers advantages in nano-photonic devices due to its compatibility with integrated circuits. We perform detailed first-principles calculations to investigate the electro-optic effect in Al_1-xSc_xN alloys and superlattices. At elevated Sc concentrations in alloys, the EO coefficients increase; importantly, we find that cation ordering along the c axis leads to enhanced EO response. Strain engineering can be used to further manipulate the EO coefficients of AlScN films. With applied in-plane strains, the piezoelectric contributions to the EO coefficients increase dramatically, even exceeding 250 pm/V. We also explore the possibility of EO enhancement through superlattice engineering, finding that nonpolar a-plane (AlN)_m/(ScN)_n superlattices increase EO coefficients beyond 40 pm/V. Our findings provide design principles to enhance the electro-optic effect through alloy engineering and heterostructure architecture.