Scalable van der Waals photonics: High-refractive-index gallium sulfide films with single-crystal optical properties

Abstract

The integration of high-refractive-index dielectrics into scalable photonic architectures is foundational to advancing integrated circuits and augmented reality displays. Van der Waals (vdW) materials offer exceptional optical properties, including high refractive indices and giant anisotropy, but their implementation is constrained by the small area and uncontrolled thickness of mechanically exfoliated flakes. Here, we demonstrate that atomic layer deposition grown gallium sulfide (GaS) films overcome the trade-off between high optical performance and manufacturability, emerging as a large-scale vdW dielectric platform. Through rigorous optical and structural benchmarking against pristine single crystals, we establish that the optical constants (n, k) of GaS films are virtually indistinguishable from those of single-crystal counterparts. By leveraging the out-of-plane anisotropy, we demonstrate that large-scale GaS enables superior suppression of crosstalk in densely integrated waveguides compared to conventional scalable high-index platforms. Our findings establish scalable GaS as a technologically viable pathway for implementing anisotropic vdW materials in visible-spectrum photonics.