Local structure of amorphous GeTe and PdGeSbTe alloy for phase change optical recording

The local structures of amorphous Ge0.52Te0.48 and Pd0.01Ge0.17Sb0.26Te0.56 were examined by extended x-ray absorption fine structure. In amorphous GeTe film, only Ge atoms were observed in the nearest-neighbor of Te atoms. The average coordination number around Te atoms in amorphous GeTe is 1.5 which is close to twofold coordination. These results support a chemically ordered structure model. In amorphous PdGeSbTe film, Ge and Sb (and/or Te) atoms were observed in the nearest-neighbor of Te atoms at distances of 2.61 and 2.84 Å, respectively. Debye–Waller factors of the Te–Ge bonds in TeGe and PdGeSbTe are 0.076 and 0.081 Å, respectively, and are larger than that of Te-(Sb and/or Te); 0.063 Å. From these results, we argue that the softened Te–Ge bond plays an important role in the elementary process of crystallization of GeTe and PdGeSbTe alloys. The total average coordination number of Pd atoms in amorphous PdGeSbTe alloy is 4.0. This result suggests Pd atoms play the role of cross-linking element.