Inter-diffusion of Plasmonic Metals and Phase Change Materials

This work investigates the problematic diffusion of metal atoms into phase change chalcogenides, which can destroy resonances in photonic devices. Interfaces between Ge2Sb2Te5 and metal layers were studied using X-ray reflectivity (XRR) and reflectometry of metal-Ge2Sb2Te5 layered stacks. The diffusion of metal atoms influences the crystallisation temperature and optical properties of phase change materials. When Au, Ag, Al, W structures are directly deposited on Ge2Sb2Te5 inter-diffusion occurs. Indeed, Au forms AuTe2 layers at the interface. Diffusion barrier layers, such as Si3N4 or stable diffusionless plasmonic materials, such as TiN, can prevent the interfacial damage. This work shows that the interfacial diffusion must be considered when designing phase change material tuned photonic devices, and that TiN is the most suitable plasmonic material to interface directly with Ge2Sb2Te5.Comment: 23 pages, 8 figures, articl

Electric field effects in chalcogenides

The objective of this paper is to demonstrate that Ag readily diffuses into Sb2S3 and that electric fields can control the diffusion. Ag diffusion influences the crystallization temperature and electrical properties of Sb2S3. We studied the interface between Ag and Sb2S3 using X-ray reflectivity and show that the Ag cations can be controlled by applying an electric field. We believe this effect has technological applications in data storage devices.</p

Design of a 4-level active photonics phase change switch using VO 2

The objective of this work is to design and demonstrate multilevel optical switches by combining different phase change materials. Ge2Sb2Te5 and VO2 nanolayer structures were designed to maximize the optical contrast between four different reflective states. These different optical states arise due to the independent structural phase transitions of VO2 and Ge2Sb2Te5 at different temperatures. The transfer matrix method was used to model Fresnel reflection for each structural phase combination and then to optimize the VO2 and Ge2Sb2Te5 layer thicknesses, which were found to be 70 nm and 50 nm. These multilevel optical switching results provide further possibilities to design composite materials for applications in active and programmable photonics.NRF (Natl Research Foundation, S’pore)ASTAR (Agency for Sci., Tech. and Research, S’pore)MOE (Min. of Education, S’pore)Published versio