Crystal structure assessment of Ge–Sb–Te phase change nanowires

Abstract

Further improvement of phase change memory devices based on Ge–Sb–Te alloys imposes the reduction of the active cell dimensions to the nanoscale. We investigate the atomic arrangement of Ge₁Sb₂Te₄ and Ge₂Sb₂Te₅ nanowires. We identify the stacking sequence in each crystal structure by combining the direct observation by High Angle Annular Dark Field imaging and proper simulations. We find out that Ge and Sb atoms randomly share the same lattice sites, although this configuration is considered not stable according to the existing theoretical models elaborated for the bulk material.