Crystallization and phase separation in Ge2+xSb2Te5 thin films

The electrical properties and the structure of isothermally annealed thin films of Ge2+xSb2Te5 (x=0 and 0.5) have been studied by in situ electrical measurements, x-ray diffraction, and transmission electron microscopy analyses. Phase separation has been observed in samples with an excess of Ge; by annealing amorphous Ge2.5Sb2Te5 films at temperatures in the range 130-160 degreesC, the material cannot be completely converted into the metastable face-centered-cubic (fcc) structure. At temperatures higher than 160 degreesC, the residual amorphous material may be converted into a fcc structure with a lower lattice parameter.