R&D: Influence of Underlayer on Crystallization of Thin Ge-rich Ge–Sb–Te Films

Journal of Applied Physics has published an article written by Philipp Hans, Aix Marseille Univ, Univ Toulon, CNRS, IM2NP UMR 7334, Marseille, France, Thomas Fernandes, Aix Marseille Univ, Univ Toulon, CNRS, IM2NP UMR 7334, Marseille, France, and STMicroelectronics, 850 rue Jean Monnet, 38920 Crolles, France, Cristian Mocuta, Synchrotron SOLEIL, L’Orme des Merisiers, Départementale 128, 91190 Saint-Aubin, France, Solène Comby-Dassonneville, Michael Texier, Aix Marseille Univ, Univ Toulon, CNRS, IM2NP UMR 7334, Marseille, France, Gabriele Navarro, CEA LETI, Univ. Grenoble Alpes, 38000 Grenoble, France, Yannick Le-Friec, Simon Jeannot, STMicroelectronics, 850 rue Jean Monnet, 38920 Crolles, France, and Olivier Thomas, Aix Marseille Univ, Univ Toulon, CNRS, IM2NP UMR 7334, Marseille, France.

Abstract: “Ge-rich Ge–Sb–Te alloys exhibit a high (>350°C) crystallization temperature, which is compatible with applications requiring a high thermal stability such as the use of non-volatile memories in cars. As the composition of these alloys does not correspond to any stable crystalline phase, crystallization from the amorphous phase is accompanied by phase separation (Ge₂Sb₂Te₅ + Ge). The complexity of the elemental processes associated with this multiphase amorphous-to-crystal transition calls for in-depth materials studies. In this work, we focus on the influence of a thin (5 nm) underlayer (Ge₂Sb₂Te₅ or Sb₂Te₃) on the crystallization of a Ge-rich Ge–Sb–Te alloy. Using in situ synchrotron x-ray diffraction, we demonstrate that the underlayers facilitate crystallization by decreasing crystallization temperature and suppressing incubation time. These results are interpreted in the framework of classical nucleation theory and are supported by crystallographic texture measurements, which evidence ⟨ 111 ⟩ fiber texture in the crystallized cubic Ge₂Sb₂Te₅, particularly marked in the case of an Sb₂Te₃ underlayer. These results bear important consequences for the cycling of memory cells based on these materials.“