Effects of biaxial strain on interfacial intermixing and local structures in strain engineered GeTe-Sb₂Te₃ superlattices

Van der Waals (vdW) layered GeTe-Sb₂Te₃ superlattices (GST-SL) have attracted enormous attentions due to the ultralow power consumption for nonvolatile phase change memory. In this paper, effects of biaxial strain on interfacial intermixing and local structures in strain engineered GST-SL were studied. Highly (0 0 l) textured GST-SL with thickness-varied Sb₂Te₃ sublayers were fabricated by magnetron sputtering and investigated with multiple analyses on surfaces and interfaces. The appearance of Ge-Sb-Te alloys indicated the interfacial Ge/Sb intermixing in strain engineered GST-SL, which actually were composed of Sb₂Te₃ quintuple layers, Ge-Sb-Te vdW layers and isolated GeTe bilayers. Grazing incidence x-ray diffraction (GID) and x-ray photoelectron spectroscopy (XPS) results revealed that biaxial strain not only facilitated the interfacial intermixing, but also caused the reconfiguration of Ge-Sb-Te vdW layers. Raman spectra indicated that vertical and in-plane vibrations of GeTe layers were not affected by the interfacial intermixing and the newly-formed Ge-Sb-Te layers had similar vibration characteristics as that of GeTe layers. A modified switching mechanism of GST-SL, relating to both the amorphous-crystalline phase transition of GeTe and Ge-Sb-Te layers incorporated into the Sb₂Te₃ matrix, was then presented. The present studies shed new light on strain engineering for GST-SL and indicate their potential optoelectronic applications.