Atomistic simulations of the decomposition pathways of Ge-rich GeSbTe alloys for phase change embedded memories

The prototypical Ge2Sb2Te5 phase change compound employed for phase change memories display a crystallization temperature two low for embedded memories of interest for automotive applications. Ge-rich GeSbTe (GST) alloys are emerging as a promising material for these applications thanks to the higher thermal stability of the amorphous phase. Upon crystallization Ge-rich GST alloys undergo a phase separation into Ge and a less Ge-rich GST alloy. This phase separation enhances the crystallization temperature, but it also gives rise to some drawbacks such as a high cell-to-cell variability and a drift of the electrical resistance with time in the set state. The details of the decomposition process are, however, still largely unknown. In this work, we report on a high-throughput screening based on Density Functional Theory calculations of the decomposition pathways of Ge-rich GST alloys. We calculated the formation free energy of GST alloys in the central region of Ge-Sb-Te ternary phase diagram. These data allowed us to estimate the decomposition propensity of Ge-rich GST alloys which suggests a possible strategy to minimize phase separation by still keeping a high crystallization temperature.