Tailoring phase change materials for nanophotonic applications

Controlling a state of material between its crystalline and glassy phase has fostered many real-world applications. Switching between these two different states is particularly interesting if it is accompanied by a significant change of optical properties. Phase change materials provide the interesting property combination of fast switching between these two states which is accompanied by a pronounced property change. For nanophotonic applications it is crucial to tailor the crystallization kinetics, the relevant length scale of the switching processes as well as the optical contrast. In this presentation, we will devise design rules for crystallization and vitrification kinetics, control of the nanostructure as well as the contrast of the corresponding optical properties. We present a clear stoichiometry dependence of optical properties and crystallization speed. The stoichiometry dependence is correlated with material properties, such as the optical properties of the crystalline phase and a bond indicator, the number of electrons shared between adjacent atoms. A quantum-chemical map explains these trends and provides a blueprint to design crystallization kinetics.