No abstract

Ge-rich GeSbTe alloys allowed overcoming temperature limitations of Phase-Change Memory technology. In this paper, we present a thorough investigation of the structural evolution and crystallization process of these alloys as a function of increasing temperature of annealing. We highlight the progressive rearrangement of the structure towards the demixing of Ge and GeSbTe phases. In particular, we show the stability of Sb-Te units and the development of Ge-Te bonds around these features. We observe the formation of a transient GeSbTe phase, which is driven by crystallization phenomena, leading to a gradual diffusion and expulsion of Ge. Therefore, the system moves towards the complete separation of Ge and Ge2Sb2Te5 stable phases. Furthermore, we investigate the effect of N doping in Ge-rich GeSbTe, which induces the formation of Ge-N bonds. Such features are demonstrated to be responsible for a delayed structural reorganization to higher temperatures, thus affecting the entire process of crystallization and phase separation in the alloy.