Determination of the glass transition and nucleation temperatures in Ge₂Sb₂Te₅ sputtered films

Amorphous Ge₂Sb₂Te₅ films were prepared by rf sputtering from the bulk alloy. Their electrical and optical properties were analyzed using impedance and optical transmission measurements as a function of temperature. From this analysis, it is found that the glass transition temperature of the as-prepared amorphous films is of about 100°C. This result is confirmed by calorimetric measurements. Impedance and optical measurements in films measured at temperatures between the glass transition and the crystallization temperatures show the appearance of the nucleation centers. Using models for two-phase materials, the electrical parameters of the crystalline and amorphous phases were estimated and related with structural parameters of the samples.