Electrical properties and crystal structures of nitrogen-doped Ge ₂Sb₂Te₅ thin film for phase change memory

The characteristics of nitrogen-doped Ge₂Sb₂Te ₅ thin films deposited on Si (100) substrates were investigated by X-ray diffraction (XRD) analysis, four-point probe and atomic force microscopy (AFM). It was found that the sheet resistance of the films annealed at 260 and 300°C increased and the face-centered cubic (fcc) peaks of crystalline state of the films gradually disappeared with the increase of N₂ gas flow rate. At the N₂ gas flow rate of 12 sccm, however, the sheet resistance of the film remarkably dropped to around that of crystalline state of undoped film and the crystal structure transformed from fee to hexagonal. The RMS roughness values of the films decreased by the nitrogen doping. However, the surface of the film deposited at the N₂ gas flow rate of 12 sccm was very rough due to crystallization of the film into hexagonal when the film was annealed at 260°C for 20 min.