Change in Structure of Amorphous Sb–Te Phase-Change Materials as a Function of Stoichiometry

Chalcogenide phase-change materials (PCMs) are a leading candidate for non-volatile memory and neuro-inspired computing applications. Antimony telluride alloys can be made into fast and robust PCMs by proper doping. Depending on the compositional ratio, the amorphous state of these alloys shows either nucleation- or growth-driven crystallization dynamics at elevated temperatures. In this work, thorough ab initio simulations are carried out to study the structural properties and bonding nature of six Sb–Te alloys with varied composition from 2:3 to 4:1. Despite all of the compounds showing similar local structural motifs consisting of defective octahedral configurations, a gradual change in medium range order and cavity concentration is observed as the Sb content increases. This trend is responsible for the reduction in the nucleation rate, thus leading to growth-driven crystallization. In addition, the degree of charge transfer decreases as the composition approaches the Sb end, reducing the driving force for long-term mass transport and phase separation upon extensive cycling in devices.