Crystal structure and microstructure of nitrogen-doped Ge2Sb2Te5 thin film

Ge2Sb2Te5 thin film is a promising candidate for recording material of phas e-change optical disks, and nitrogen is doped into this rilm to increase ov erwrite characteristics. hi this study, the crystal structure and the micro structure of nitrogen-doped Ge2Sb2Te5 thin film were investigated. In the a nnealed nitrogen-doped thin film, the characteristic face-centered cubic pe aks on the X-ray diffraction pattern were broadened and shifted to a smalle r angle with the increase of nitrogen content. In addition, a remarkably re duced grain size and a highly strained structure are seen in the transmissi on electron microscopy image. Doped nitrogen in Ge2Sb2Te5 thin film plays t wo roles. One is to distort the crystal lattice and induce a strain field i n the film. The other is to refine the grain size of the him through precip itation. The crystal lattice is transformed from face-centered cubic to a h exagonal structure in nitrogen content above 20 at.%.