Electron localization in recrystallized models of the Ge2Sb2Te5 phase-change memory material

Understanding the relation between the structural disorder in the atomic geometry of the recrystallized state of phase-change memory materials and the localized states in the electronic structure is necessary not only for technological advances, but also essential to achieve a fundamental understanding of these materials. In this computational study, hybrid density-functional theory simulations are employed to ascertain the impact of antisite defects on the spatial localization of the electronic states in the bottom of the conduction band in recrystallized models of the prototypical phase-change material ${\mathrm{Ge}}₂{\mathrm{Sb}}₂{\mathrm{Te}}₅$. $\mathrm{Te}\text{\ensuremath{-}}\mathrm{Te}$ homopolar bonds are the local defective atomic environments mainly responsible for the electron localization of the conduction-band-edge states in the simulated structures, while $\mathrm{Sb}\text{\ensuremath{-}}\mathrm{Te}$ chains can also induce spatial localization. Unoccupied defect-related electronic states can emerge in the band gap during a crystallization event, while $\mathrm{Sb}\text{\ensuremath{-}}\mathrm{Sb}$ homopolar bonds have been identified in the defect environment of a deep localized state.