Optical memory based on GeSbTe-O alloys

The purpose of this study was to develop new active material for phase-change optical memory (Compact Disks) which would make it possible to record information with 3 or 4 levels of reflectivity and not only 2, as is the case now. With this goal in mind, the optical properties (reflectance) of Ge₁Sb₂Te₄ films doped with oxygen were investigated. X-ray diffraction shows that the crystalline phase for films with 2-8% oxygen corresponds to a Ge₁Sb₂Te₄ composition. However, the crystalline phase for films with more than 10% oxygen corresponds to Sb₂Te₃. This phase segregation in films containing more than 10% oxygen gives, as a result, an increase in nucleation times and in laser-induced crystallization times, making multilevel recording possible, that is to say, optical memory with ternary or quaternary code instead of just binary code.