Kombinatorische PVD-Synthese und Strukturuntersuchungen der Ge-Sb-Te-Schichten
In this work a mapping of the structure and structural change of metastable and stable phases of the ternary Ge-Sb-Te system was realized in a wide composition range including the quasi binary line GeTe-Sb2Te3. Therefore homogeneous films and films with a compositional gradient were deposited using a combinatorial PVD technique (magnetron sputtering). The samples with a compositional gradient up to 20 at. % had the following composition in the centre: Ge1Sb4Te7, Ge1Sb2Te4, Ge2Sb2Te5, Ge3Sb2Te6, and Ge4Sb1Te5. The films' structure was analyzed using X-ray diffraction with high lateral resolution. The structural mapping of the films was conducted as a function of the composition after the films' tempering at different temperatures (200°C, 300°C, and 400°C) in order to determine the phase change with temperature. Thermally induced, the deposited amorphous Ge-Sb-Te films changed at first to the metastable cubic phase, and with increasing temperature to the stable hexagonal phase. Between the regions of cubic and hexagonal phases the formation of a transition region with both phases was observed. During the phase change the phases were separated in general by the quasi binary line, which could be explained by phase separation of hexagonal Te. Since this phase separation was found only in the stable hexagonal phase of Ge-Sb-Te, the phase separation of Te is supposed to be a nucleation source for the amorphous-to-hexagonal phase change in the films. Phase separation of Ge was found only in the Ge-rich edge after tempering at 400°C. Ge and Te in the regions outside the quasi binary line was formed and remained as an amorphous phase in the metastable cubic phase of Ge-Sb-Te. The lattice parameter mapping of the cubic and hexagonal phases showed a continuous decrease of the lattice parameters from the Sb2Te3 towards the GeTe-side and is in concordance with literature data for the single stoichiometric compounds. The microstructure mappings on the basis of full width at half maximum (FWHM) showed for the cubic phase the formation of a region with a constant microstructure beginning from Ge2Sb2Te5 up to the edge of the GeTe-side. This region was characterized at the same time by the highest phase change velocities of the as deposited amorphous phase. The results were obtained by the comparison with phase change dynamic experiments and indicate the higher nucleation or crystallites growth rate. The comparison of the mappings of the phase change and the phase change velocities showed that the region with the higher phase change velocities is not symmetric to the quasi binary line according to literature data, but is shifted to the Ge-rich-side. Furthermore, since the region of the low phase change velocities has a good overlapping with the region of the Te phase separation, this indicates the formation of a mixed phase of Te and a hexagonal Ge-Sb-Te phase during the laser induced phase change. Such a multistage phase change amorphous-cubic-hexagonal+Te may cause the reduction of the phase change velocities.
info:eu-repo/classification/ddc/620, Germanium, Antimon, Technetium, Dünne Schicht, Kombinatorische Synthese, PVD-Verfahren, Ternäres System, Funktioneller Gradientenwerkstoff, Optischer Speicher, Ingenieurwissenschaften, Kombinatorische Schichtsynthese, Magnetronsputtern, Ge-Sb-Te
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