Atomistic effect on infrared dielectric response of GaN/AlN superlattices

Polar dielectric superlattices are a promising platform for tailoring infrared nanophotonics. However, both the physics and modeling of atomistic effects on their infrared optical response, especially in ultra short-period structures, are not yet established. Here, we investigate the infrared dielectric properties of GaN/AlN superlattices via an atomistic framework based on machine-learning molecular dynamics with dynamic charges. By accounting for the delocalized nature of phonons in alternate layers and long-range electrostatic interaction, we provide a quite good prediction of the infrared dielectric function and reflectance of short-period (GaN)5(AlN)4 and (GaN)9(AlN)9 superlattices. Furthermore, we systematically demonstrate tunable frequencies of infrared phonon modes with composition ratio and their transition with increasing period size. This work thus provides fundamental insights into the atomistic mechanisms governing infrared optical properties in polar superlattices and offers an efficient platform for designing infrared optoelectronic devices.