Unraveling Crystal Growth in GeSb Phase-Change Films in between the Glass-Transition and Melting Temperatures

Abstract

The study of crystal growth in phase-change thin films is of crucial importance to improve our understanding of the extraordinary phase transformation kinetics of these materials excellently suited for data storage applications. Here, we developed and used a new method, based on isothermal heating using laser illumination in combination with a high-speed optical camera, to measure the crystal growth rates, in a direct manner over 6 orders of magnitude, in phase-change thin films composed of several GeSb alloys. For Ge8Sb92 and Ge9Sb91, a clear non-Arrhenius temperature dependence for crystal growth was found that is described well on the basis of a viscosity model incorporating the fragility of the supercooled liquid as an important parameter. Using this model, the crystal growth rate can be described for the whole range between the glass transition temperature of about 380 K and the melting temperature of 880 K, excellently explaining that these phase-change materials show unique and remarkable behavior that they combine extremely low crystal growth rates at temperatures below 380 K required for 10 years of data retention and very fast growth rates of 15 m s–1 at temperatures near the melting point required for bit switching within tens of nanoseconds.