The amorphous-to-crystal transition has been studied through in situ resistance measurements in Ge2Sb2Te5 thin films doped by ion implantation with nitrogen or oxygen. The dependence of the electrical resistivity and structure on the annealing temperature and time has been investigated in samples with different dopant concentrations. Enhancement of the thermal stability and increase of the mobility gap for conduction have been observed in O- and N-doped amorphous Ge2Sb2Te5. Larger effects have been found in the case of nitrogen doping.

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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 °C, the material cannot be completely converted into the metastable face-centered-cubic (fcc) structure. At temperatures higher than 160 °C, the residual amorphous material may be converted into a fcc structure with a lower lattice parameter.

The kinetics of the amorphous-to-crystal transition in Ge2Sb2Te5 thin films have been studied through in situ transmission electron microscopy analyses. By following the time evolution of the grain density and size, the growth velocity and the nucleation rate have been separately measured at different annealing temperatures. Activation energies of 2.9±0.5 eV and 2.3±0.4 eV have been obtained for the nucleation rate and the growth velocity, respectively. The barrier energy for the nucleation of a critical nucleus ΔG* has been evaluated, and the scalability of phase change nonvolatile memories has been estimated.

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