Structural and electronic characteristics of amorphous Ge8Sb2Te11

GeTe-rich phase-change materials can be utilized in rewriteable optical memory due to the large contrast in reflectivity between amorphous and crystalline phases. Here we explored the structure and electronic properties of amorphous Ge ₈Sb ₂Te ₁₁ using ab initio molecular dynamics simulations. The results indicate that amorphous Ge ₈Sb ₂Te ₁₁ is dominantly composed of Ge-, Sb- and Te-centered octahedrons with distortions, while 30.4 % of Ge-centered clusters are in the form of tetrahedrons which are randomly distributed. The 5-fold rings possess a large proportion, and the Ge Te and Sb Te bonds present larger formation energies than other bonds, leading to the ABAB bonding sequence (A: Ge and Sb, B: Te). The lone pair electrons locating at the opposite direction of bonds possess a large fraction of 14.8 %, which may enhance the distortions of local clusters. These structural properties lead to the high stability of amorphous Ge ₈Sb ₂Te ₁₁ and thus long data retention in the information storage.