Atomic Imaging of Layered Structure Phase-Change Materials

Fast and reversible phase transitions in chalcogenide phase-change materials (PCMs), in particular, Ge-Sb-Te (GST) compounds, are not only of fundamental interests but also make PCMs based random access memory a leading candidate for nonvolatile memory, and neuromorphic computing devices. Disorder plays an essential role in shaping the transport properties of GST. Recently, increasing efforts have been undertaken to investigate disorder in the layer-structured GST compounds. In this work, we focus on hexagonal GST. We thoroughly characterized the structural and chemical features of the major defects in hexagonal GST at atomic scale through chemi-scanning transmission electron microscopy (STEM) experiments, including the stacking faults, the in-plane and out-plane twin-like structure, and a unique bilayer structure. By combining nanoscale density functional theory (DFT) modelling and simulations, we clarified the underlying reasons of the abundance of these defects and their effects on the electronic and transport properties of hexagonal GST.