Exploring mechanism on nano-structuring manipulation of crystallization temperature of superlattice-like GeSb/Ge_3 phase-change films

摘要

Superlattic-like phase-change films are considered a promising phase-change material because it provides more controllable degree of freedoms for the simultaneous optimization of multiple parameters of phase-change films. However, the mechanism on the effect of superlattice-like structure on parameters of phase-change films is still controversial. At present there are two opinions: interfacial effect and the reduction of thermal conductivity. Here four superlattice-like phase-change films, [Ge_8Sb_(92)(15 nm)/Ge (x nm)]_3, are fabricated. Their behaviors of crystallization are investigated using the measurements of sheet resistance and coherent phonon spectroscopy. Two measurements show the crystallization temperature of the four superlattice-like films increases with the thickness of Ge layers. However, this increase cannot be explained by both the interfacial effect and the reduction of thermal conductivity. It is proposed that true superlattice effect should be considered to explain the effect of superlattice-like structure. Electron diffusion between two different constituent layers should be considered, as done in semiconductor superlattice structures. Electron diffusion can lead to the establishment of built-in electric field inside the superlattice-like films, which causes the change of band structures of two constituent materials and long-range coupling of superlattice-like films, further change of physical parameters. Based on this long-range coupling, the effect of cycle number in superlattice-like films on crystallization temperature can be explained. Some primary evidence on electric field effect on crystallization temperature of phase-change films is provided.