Double optical phase transition of GeSbTe thin films sandwiched between two SiN layers

Crystallization mechanism of Ge2Sb2Te5 thin films sandwiched between SiN layers was optically investigated and double transition temperatures were observed in the case of Ge2Sb2Te5 film thickness of more than 20 nm. The activation energies were estimated by both Kissinger's and Johnson-Mehl-Avrami equations, and it was found that the reaction order was 2 for the first crystallization and 1 for the second transition. The lower transition temperature was strongly affected by the top SiN film thickness, and it was suggested that crystallization occurred at the interface between the recording film and the top SiN layer. The second crystallization occurred at the interface between the bottom SiN and the recording layers, which was not greatly affected by the thicknesses of both films.