Thermal characterization of Se–Te thin films

Abstract

The thermal behavior of thin selenium–tellurium (Se–Te) films was studied under non-isothermal conditions using differential scanning calorimetry; full binary compositional range was investigated. Based on the glass transition, crystallization and melting data the decreasing glass-forming ability in the Se–Te chalcogenide system was described by using a novel glass-forming ability (GFA) criterion. The glass transition kinetics of the as-prepared thin films was found to change with increasing Te content; namely the activation energy of structural relaxation processes decreased from 355 to 245kJmol−1 within the given compositional region. In the glass-forming region (at approx. 0–30% Te) the GFA and relaxation data obtained for the thin films correlated very well with the results for bulk glasses. Furthermore, the kinetics of crystallization were studied and described in terms of the Johnson–Mehl–Avrami nucleation-growth model. The apparent activation energy of crystallization was found to increase with Te content, changing from 115 to 170kJmol−1 in the given compositional range. Two-dimensional growth of crystallites, consistent with the idea of sterically restricted crystallization in a thin layer, was confirmed for the Se-rich compositional region. Further addition was found to lead to increased process complexity due to the formation of smaller, volume-located crystallites. In the glass-forming region, the crystallization kinetics of thin films corresponded to that determined for very fine Se–Te powders.