Inter-diffusion of plasmonic metals and phase change materials

This work investigates the diffusion of metal atoms into phase change chalcogenides, which is problematic because it can destroy resonances in photonic devices. Interfaces between Ge ₂Sb ₂Te ₅ and metal layers were studied using X-ray reflectivity and reflectometry of metal–Ge ₂Sb ₂Te ₅ 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 Ge ₂Sb ₂Te ₅, inter-diffusion occurs. Indeed, Au reacts with Ge ₂Sb ₂Te ₅ to form a AuTe ₂ layer at the interface. Diffusion barrier layers, such as Si ₃N ₄ or stable 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 Ge ₂Sb ₂Te ₅.