The nature of the crystallization nuclei in Ge2Sb2Te5 alloys

Using two independent methods of investigation (impedance and X-ray diffraction measurements), it is shown that the crystallization process in amorphous Ge2Sb2Te5 thin films starts below the actual crystallization temperature Tc of this material. The nucleation centers, which appear at annealing temperatures around 120 °C, are identified with the crystalline fcc Ge1Sb4Te7 phase. When the sample temperature increases above Tc, these nuclei are transformed into Ge2Sb2Te5 fcc crystals. The volume fraction of nuclei, their size and electric characteristics are found.