The effect of Ge content on structural evolution of Ge-rich GeSbTe alloys at increasing temperature

The material engineering of GeSbTe alloys has led to the significant improvements of thermal stability, necessary to ensure the data retention of the Phase-Change Memory device (PCM) over extended temperature range. However, despite the proven benefits of Ge enrichment of GeSbTe alloys, the effect of Ge content on the structure and its evolution as a function of annealing temperature remains unclear. In this paper, we present the structural analyses of as-deposited and annealed Ge-rich GeSbTe, considering the Ge enrichment (15–55 at.%) of reference Ge2Sb2Te5 alloy. Based on the combination of Raman spectroscopy and X-ray diffraction techniques, we describe the progressive reorganization of the main structural features common to all investigated compositions. Therefore, we present a model describing the overall crystallization mechansim in Ge-rich GeSbTe. We highlight several competing phenomena in the system at increasing temperature, such as Ge diffusion and segregation as well as nucleation and growth of GeSbTe and Ge phases, which depends on Ge content. Our results contribute to the understanding of the crystallization mechanisms in Ge-rich GeSbTe alloys, unveiling the primary structural reorganization and crystallization of the GeSbTe phase followed by the crystallization of the Ge phase.