Towards higher electro-optic response in AlScN

TL;DR

This paper investigates how alloy composition, cation ordering, strain, and superlattice architecture can significantly enhance the electro-optic response of AlScN materials, offering design principles for advanced photonic devices.

Contribution

It provides first-principles insights into how alloying, cation ordering, strain, and superlattice structures can be used to increase the electro-optic coefficients of AlScN.

Findings

EO coefficients increase with higher Sc concentration.

Cation ordering along the c axis enhances EO response.

Strain engineering can dramatically boost EO coefficients, exceeding 251 pm/V.

Abstract

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 $\mathrm{Al}_{1-x}\mathrm{Sc}_{x}\mathrm{N}$ 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 251 pm/V. We also explore the possibility of EO enhancement through superlattice engineering, finding that nonpolar $a$-plane $\mathrm{(AlN)}_m/\mathrm{(ScN)}_n$ 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.