First-principles study of amorphousGa4Sb6Te3phase-change alloys

Abstract

First-principles molecular dynamics simulations within the density functional theory framework were performed to generate amorphous models of the ${\mathrm{Ga}}_{4}{\mathrm{Sb}}_{6}{\mathrm{Te}}_{3}$ phase change alloy by quenching from the melt. We find that Ga-Sb and Ga-Te are the most abundant bonds with only a minor amount of Sb-Te bonds participating to the alloy network. Ga and four-coordinated Sb atoms present a tetrahedral-like geometry, whereas three-coordinated Sb atoms are in a pyramidal configuration. The tetrahedral-like geometries are similar to those of the crystalline phase of the two binary compounds GaTe and GaSb. A sizable fraction of Sb-Sb bonds is also present, indicating a partial nanoscale segregation of Sb. Despite the fact that the composition ${\mathrm{Ga}}_{4}{\mathrm{Sb}}_{6}{\mathrm{Te}}_{3}$ lies on the pseudobinary $\mathrm{Ga}\mathrm{Sb}\ensuremath{-}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ tie line, the amorphous network can be seen as a mixture of the two binary compounds GaTe and GaSb with intertwined elemental Sb.