Crystal Structure and Microstructure of Nitrogen-Doped Ge₂Sb₂Te₅ Thin Film

Ge₂Sb₂Te₅ thin film is a promising candidate for recording material of phase-change optical disks, and nitrogen is doped into this film to increase overwrite characteristics. In this study, the crystal structure and the microstructure of nitrogen-doped Ge₂Sb₂Te₅ thin film were investigated. In the annealed nitrogen-doped thin film, the characteristic face-centered cubic peaks on the X-ray diffraction pattern were broadened and shifted to a smaller angle with the increase of nitrogen content. In addition, a remarkably reduced grain size and a highly strained structure are seen in the transmission electron microscopy image. Doped nitrogen in Ge₂Sb₂Te₅ thin film plays two roles. One is to distort the crystal lattice and induce a strain field in the film. The other is to refine the grain size of the film through precipitation. The crystal lattice is transformed from face-centered cubic to a hexagonal structure in nitrogen content above 20 at.%.