Discovery of the GeSbTe phase-change alloy in particular along the GeTe–Sb2Te3 tie-line took place in the mid-1980s. The amorphous alloys showed ideal properties, for example, high thermal stability at r.t. and laser-induced rapid crystallization with large optical changes. Thereafter, GeSbTe was successively applied to various optical disks such as DVDs and BDs. Through DSC and XRD analyses, the appearance of the metastable phase having a NaCl-type structure was observed over a wide compositional region. This was the “key” to realizing the ideal phase-change properties. During this year, the role of the constituent elements of Ge and Sb became clear by RMC modeling using AXS data at SPring-8, where the “nucleation dominant crystallization process” was well explained.
The aspect of the latest Blu-ray Disc (BD) product of Panasonic: GeSbTe phase-change films are utilized in every recording layer. It is seen that the front-side recording layers, L1 and L2, are highly transparent.