Atomistic Modeling of Charge-Trapping Defects in Amorphous Ge-Sb-Te Phase-Change Memory Materials

Understanding the nature of charge-trapping defects in amorphous chalcogenide alloy-based phase-change memory materials is important for tailoring the development of multilevel memory devices with increased data storage density. Herein, hybrid density-functional theory simulations have been employed to investigate electron- and hole-trapping processes in melt-quenched glassy models of four different Ge-Sb-Te compositions, namely, GeTe, Sb₂Te₃, GeTe₄, and Ge₂Sb₂Te_5. The calculations demonstrate that extra electrons and holes are spontaneously trapped, creating charge-trapping centers in the bandgap of the amorphous materials. Over- and undercoordinated atoms, tetrahedral and “see-saw” octahedral-like geometries, fourfold rings, homopolar bonds, near-linear triatomic configurations, and chain-like motifs comprise the range of the defective atomic environments that have been identified in the structural patterns of the charge-trapping sites inside the glassy networks. The results illustrate that charge trapping corresponds to an intrinsic property of the glassy Ge-Sb-Te systems, show the impact of electron and hole localization on the atomic bonding of these materials, and they may have important implications related to the operation of phase-change electronic-memory devices.