Phase change materials (PCM), based on Ge-Sb-Te alloys, are among the most auspicious classes of materials for both optical and electrical storage applications. To further develop PCM technology for electrical memory, it is crucial to clearly identify the structural defects present in such alloys and further on to understand their role in electrical transport.
Ferhat Katmis et al. (pp. 769–773) investigated the structural evolution of Ge-Sb-Te alloys by synchrotron-based X-ray scattering in situ during molecular beam epitaxy and also ex situ. The results reveal the formation and evolution of defect-induced inhomogeneities during growth. Long-range crystal-lattice distortion fi elds are generated by point defects formed during the growth with an average range of the distortion fi eld around the defect of about 2.5–3.0 nm and a pronounced fi eld anisotropy. In contrast to the well-known structural model, in which random occupation of Ge (octahedrally bonded), Sb, and vacancies on the cation site creates an isotropic distortion fi eld, the experimental results point to the presence of defects caused by a fraction of tetragonally bonded Ge atoms.