Electric-field-induced annihilation of localized gap defect states in amorphous phase-change memory materials. (15th January 2022)

• Record Type: Journal Article
• Authors: Konstantinou, Konstantinos; Mocanu, Felix C.; Akola, Jaakko; Elliott, Stephen R.
• Is Part Of: Acta materialia. Volume 223(2022)
• Publication Date: 2022-01-15
• Subjects: Phase-change memory -- Amorphous materials -- Electric field -- Defects -- First-principles calculations; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2021.117465
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: Structural relaxation of amorphous phase-change-memory materials has been attributed to defect-state annihilation from the band gap, leading to a time-dependent drift in the electrical resistance, which hinders the development of multi-level memory devices with increased data-storage density. In this computational study, homogeneous electric fields have been applied, by utilizing a Berry-phase approach with hybrid-density-functional-theory simulations, to ascertain their effect on the atomic and electronic structures associated with the mid-gap states in models of the prototypical glassy phase-change material, Ge2 Sb2 Te5 . Above a threshold value, electric fields remove spatially localized defects from the band gap and transform them into delocalized conduction-band-edge electronic states. A lowering of the nearest-neighbor coordination of Ge atoms in the local environment of the defect-host motif is observed, accompanied by a breaking of 4-fold rings. This engineered structural relaxation, through electric-field tuning of electronic and geometric properties in the amorphous phase, paves the way to the design of optimized glasses. Graphical abstract: Image, graphical abstract