The development of innovative Non-Volatile Memory technologies (NVM) has become crucial as the amount of data required to be stored and processed is rapidly increasing. Among the several innovative NVM candidates, the Phase Change Memory (PCRAM) demonstrated to be the most promising one, providing the solutions in the domain of stand alone (e.g., Storage Class Memory) and embedded (e.g., microcontrollers) applications. PCRAM device structure is based on phase-change material integrated between two electrodes and undergoing the amorphous-to-crystalline phase change transition. The material engineering of such an integrated material plays the fundamental role in PCRAM device performances. In recent years, Ge-enriched or Nitrogen-doped GeSbTe (GST) alloys have demonstrated high thermal stability allowing the PCRAM device applications in the high-demanding automotive domain. Although the outstanding performances of PCRAM device with such integrated material have been reported, the deep investigation of material structure is still missing and the full understanding of crystallization mechanisms in such alloys represents a very active research topic.This work aims at the thorough structural investigation of GST phase-change alloys targeting the high temperature stability. We study two main groups of materials: Ge, Sb and Te elemental systems and Ge-rich GST alloys. First, we focus on the characterization of the material structure and its evolution as a function of controlled thermal budget. Then, we report on the effect of Nitrogen (N) doping. We combine optical (Raman and Fourier transform infrared spectroscopy) and X-ray (X-ray diffraction, X-ray absorption spectroscopy) characterizations along with transmission electron microscopy and “ab initio” simulations in order to provide a complete and unique insight of the material structure. The investigation of Ge-rich GST alloys allows to describe several phenomena occurring during the crystallization process (i.e., Ge atoms diffusion, GST and Ge phases segregation, their nucleation and growth) and their dependence on Ge content in the alloy. The studies of elemental systems upon N doping present the effect of N incorporation on Ge, Sb and Te structure and describe the formation of N bonding. The results from N-doped elemental systems are applied to evaluate the N impact on the structure of complex Ge-rich GST alloys. The results of this work provide deeper understanding of GST alloys, highlighting the complementarity of used characterization techniques. Finally, future perspectives of GST alloys investigations are provided, suggesting further options of GST alloys engineering as well as the combination of characterizations, which can be employed.