Glassy transformation and structural change in Ge₂Sb₂Te₅ studied by impedance measurements

The transition form amorphous-to-crystalline (fcc) has been investigated in Ge₂Sb₂Te₅ thin film alloys. This composition is the most frequently used for erasable optical memory devices. The phase transition was monitored using in situ impedance measurements as a function of temperature. The results were analyzed using the Maxwell-Wagner and brick models. From the impedance measurements it is possible to detect the appearance of nucleation centers in samples heated at temperatures below crystallization. In samples treated at temperatures above crystallization, the increase in the volume fraction of crystalline material due to the increase in the temperature is also deduced from the impedance measurements. From our investigation we have shown that impedance measurements are a sensitive method to analyze the crystallization process in chalcogenide materials.