Thickness dependent crystallization speed in thin phase change layers used for optical recording

The erasure rate of recorded amorphous marks in nanometers thick SbTe-alloy layers is studied as a function of layer thickness. We point out the presence of an optimum layer thickness where the crystallization speed is maximized. Analysis of the Gibbs free energy of a crystallite embedded in a thin amorphous film indicates that the height of the energy barrier for crystallization is a function of phase-change layer thickness. This barrier increases steeply in thin layers due to the larger surface energy at the crystallized phase-change surface. This suggests that the crystallization speed in thin films may be improved by modifying the interfaces of the phase-change layer.