Scalable van der Waals Photonics: High-Refractive-Index Gallium Sulfide Films with Single-Crystal Optical Properties

TL;DR

This paper demonstrates that atomic layer deposition can produce large-area gallium sulfide films with optical properties matching single crystals, enabling scalable, high-performance vdW photonics for integrated optical devices.

Contribution

The study introduces ALD-grown gallium sulfide as a scalable vdW dielectric with single-crystal optical properties, overcoming previous size and thickness limitations.

Findings

ALD-GaS has optical constants similar to single crystals.

ALD-GaS enables better crosstalk suppression in waveguides.

Scalable ALD-GaS is viable for visible-spectrum photonics.

Abstract

The integration of high-refractive-index dielectrics into scalable photonic architectures is foundational to advancing integrated circuits and augmented reality (AR) 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 (ALD) grown gallium sulfide (GaS) overcomes 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 ALD-GaS are virtually indistinguishable from single-crystal counterparts. By leveraging the retained out-of-plane anisotropy, we demonstrate that ALD-GaS enables superior suppression of crosstalk in densely integrated waveguides compared to conventional scalable high-index platforms. Our findings establish ALD-GaS as a technologically viable pathway for implementing anisotropic vdW materials in visible-spectrum photonics.