Crystallization process in Ge2Sb2Te5 amorphous films

The aim of this work is to investigate the isokinetic and isothermal amorphous-to-crystalline phase transformation process in Ge2Sb2Te5 ternary alloys. The experiments were carried out using electrical impedance, X-ray diffraction and reflection measurements. The results have shown that, upon annealing, the crystallization process in amorphous Ge2Sb2Te5 films starts with nuclei which were identified as the Ge1Sb4Te7 crystalline phase. As temperature increases (or time of isothermal annealing) these nuclei are transformed into the fcc-Ge2Sb2Te5 phase. In order to establish the mechanism of crystallization for this system, a stochastic lattice model was implemented to analyze nucleation and growth of the two phases involved (i.e., the metastable Ge1Sb4Te7 nuclei followed by the stable fcc-Ge2Sb2Te5). The results of the simulations demonstrate close agreement with experimental results. Furthermore, the crystallization process in amorphous films with the Ge1Sb4Te7 composition shows the existence of only one phase during the whole process and can be described by the classical Johnson–Mehl–Avrami-Kolmogorov model.