Long-Term Structural Instabilities in Undoped 
and Nitrogen-Doped Ge2Sb2Te5 Films
We investigated the compositional, microstructural, and electrical properties of undoped and nitrogen-doped Ge2Sb2Te5 films subjected to long-term thermal annealing under air atmosphere. Considering the absence of chemical and structural changes, the sheet resistances of samples annealed at 200°C may potentially be related to changes in the lattice parameters. The disappearance of Ge–N bonds and decrease of Ge and N concentrations in samples treated at 300°C were found to depend on the cubic to hexagonal phase transition.