Investigation of phase transitions in stacked GeTe/SnTe and Ge_2Se_3/SnTe chalcogenide films

摘要

Phase transitions in stacked GeTe/SnTe and Ge_2Se_3/SnTe thin layers for potential phase-change memory applications have been investigated by X-ray diffraction using an area detector system and by scanning electron microscopy. The as-deposited underlying GeTe or Ge2Se3 layer is amorphous, whereas the top SnTe layer is crystalline. In GeTe/SnTe stack, the crystallization of GeTe phase occurs near 170°C, and upon further heating, GeTe phase disappears, followed by the formation of rocksalt-structured Ge_xSn_1_xTe solid solution. In Ge_2Se_3/SnTe stack, the phase transition starts with the separation of SnSe phase due to the migration of Sn ions into the Ge2Se3 layer. The migration of Sn ions and the formation of SnSe are believed to facilitate the crystallization of Ge_2Se_3 solid solution at ~360°C, which is much lower than the crystallization temperature of Ge_2Se_3, therefore consuming less power during the phase transition.