Crystallization Kinetics of Supercooled Liquid Ge–Sb Based on Ultrafast Calorimetry

The crystallization kinetics of phase-change materials (PCMs) entails a crucial aspect of phase-change memory technology, and their study is also of interest to advance the understanding of crystallization in general. Research on crystallization of PCMs remains challenging because of the short (nanosecond) time and small (nanometer) length scales involved. Ultrafast differential scanning calorimetry (DSC) offers a powerful tool to study crystallization via ultrahigh heating rates. Here, we used this tool to study the crystallization kinetics of growth-dominant Ge₇Sb₉₃. Two models describing the viscosity of the undercooled liquid were used to interpret the data and were subsequently crosschecked by independent growth-rate data. With both models the data in Kissinger plots could be fitted well, but one of the models resulted in a large discrepancy with the independent data. These results demonstrate that great care is needed when deriving crystal-growth rates from ultrafast DSC measurements because orders of magnitude errors can be made. The present analysis showed a slightly non-Arrhenius crystallization behavior for the Ge₇Sb₉₃ alloy, corresponding to a fragility of 65 and a glass transition temperature of 379 K. The overall viscosity and growth rate of this alloy between the glass and melting temperatures have been revealed, as well as a maximum growth rate of 21 m s^–1 at ∼800 K. Models based on ultrafast DSC data offer interpretation of crystallization kinetics of PCMs and thereby strongly support the design of PCMs for memory applications