Developing transition metal dichalcogenide alloys for applications to integrated photonics

Abstract

We explore the potential of transition metal dichalcogenides (TMDs) as phase-change materials for photonics integrated circuits (PIC). We measure the near-infrared (NIR) optical properties of bulk crystal telluride TMDs and sulfide TMDs. We find that telluride TMDs have large optical density and large optical contrast, but the loss is too high. The sulfide TMDs have lower loss, but the phase change energy is much higher. We further propose designing sulfide TMD alloys that are thermodynamically adjacent to phase boundaries between competing crystal structures, to realize martensitic (i.e., displacive, order-order) switching. We report large-area thin film synthesis of 1T TiS₂ and high-Ti-content, single-phase 2H alloy Mo₁₋ₓTiₓS₂ thin films at temperature as low as 500 °C using a scalable two-step method of metal film deposition, followed by sulfurization in an H₂S gas furnace. We demonstrate different roughening processes for each case and optimize the morphology.