Phase change in GeTe/Sb2Te3 superlattices: Formation of the vacancy-ordered metastable cubic structure via Ge migration

Interfacial phase-change memory (iPCM), comprising alternating layers of two chalcogenide-based phase-change materials-Sb2Te3 (ST) and GeTe (GT)-has demonstrated outstanding performance in resistive memories. However, its comprehensive understanding is controversial. Herein, the phase-change characteristic of iPCM is identified using atomic scale imaging, X-ray diffraction, and chemical analysis with first-principles density functional theory (DFT) calculations. By inducing laser pulsing, the ST/GT superlattice structure in the low-resistance state tends to reversibly convert into the modified metastable face-centered cubic (fcc) GeSbTe structure in the high-resistance state. This transition is driven by Ge atom rearrangement to pre-existing vacancy layers and ordered vacancy-layer formation. DFT atomistic modeling shows that the resistance difference of 10(2) orders between low- and high-resistance states is a direct consequence of the intercalation of Ge atoms into the vacancy layer. These results provide insights into iPCM phase-change mechanisms and phase-change random access memory design with low energy and high speed.

Automated summary

This study investigates the phase-change characteristics of interfacial phase-change memory (iPCM) using atomic scale imaging, X-ray diffraction, and chemical analysis with first-principles density functional theory (DFT) calculations. The results reveal that the low-resistance state of iPCM can convert reversibly into a modified metastable face-centered cubic (fcc) GeSbTe structure in the high-resistance state. This transition is driven by rearrangement of Ge atoms and formation of ordered vacancy layers. The study provides insights into the phase-change mechanisms of iPCM and the design of phase-change random access memory with low energy and high speed.