Origin of high data retention for Ge1Cu2Te3 phase-change memory

To meet the high-temperature applications of the phase change memory, Ge₁Cu₂Te₃ (GCT) has been proposed to be a suitable candidate due to its good amorphous stability. Here, we investigate the basic atomic bonding mechanism by first-principles calculations to understand this. The amorphous GCT has significant chemical disorder with large amounts of homopolar bonds. Cage-like clusters (composed of 3-fold rings) are mainly related to Cu atoms. The bonding mechanism in crystalline GCT is proposed and demonstrated by the nonequivalent sp³ hybridization with Te lone-pair electrons. In contrast, amorphous GCT requires Cu d electrons to participate in bonding due to the isolation of Te lone-pair electrons. Thus, the vast difference in atomic and electronic structures between the amorphous and crystalline phase makes the good amorphous stability for high data retention.