Compositional dependence of crystallization and structural stability in Ge-Sb-Se chalcogenide films

We systematically investigated the structural properties of as-deposited and annealed GexSbySez (x + y + z = 100, 9.5 ≤ x ≤ 59, 6.2 ≤ y ≤ 42.9, 34.8 ≤ z ≤ 51.5) chalcogenide films. For films with x < 34.5, some main SbSb homopolar bonds as well as SbSe heteropolar bonds appeared in the as-deposited films, while increasing the Ge content replaced some Se atoms, forming GeSe heteropolar bonds, which increased the optical band gap. For films with x ≥ 34.5, the structures of the as-deposited films were dominated by GeGe and SeSe homopolar bonds. The annealed Ge-Sb-Se films exhibited a phase transition from amorphous to crystalline for phase-change memory. We ascribed the crystal grains of the GexSbySez films (x = 9.5, 12.8) to be the Sb phase, while we confirmed those of the films (x = 14.2, 21.3, 22.9, 25.2) to be a mixture of Sb and Sb2Se3 phases. The films with high Ge content (x = 40.2, 59) exhibited a stable amorphous phase for optical waveguide application.