Structure analysis of amorphous thin films of GeSbTe compounds by grazing incidence X-ray scattering

We have investigated the structures of amorphous thin films of GeSbTe compounds - the materials used for the recording layer of phase-change optical memory - through grazing incidence X-ray scattering (GIXS) measurements. Thin films with compositions of GeSb2Te4 and Ge2Sb2Te5 were deposited on Si substrates. Electron radial distribution functions (RDFs) derived from the data clearly showed evidence of the medium-range order with three peaks of the atomic pair distribution. The RDFs of both samples were very similar to those of amorphous bulk GeTe compounds reported from previous X-ray scattering experiments. The positions of the first peaks of these RDFs were consistent with the distances of the first nearest neighbor pairs reported from previous EXAFS experiments. A comparison of the RDF of the amorphous phase with that of the crystalline phase suggested that the phase change caused no significant change in the number of atoms included inside or the radius of the second nearest neighbor atomic shell, although it changed the coordination number and the distance of the first nearest neighbor atomic pairs. This may shorten the moving distance of atoms in the phase change and enable high-speed phase change.