Local structure analysis of Ge-Sb-Te phase change materials using high-resolution electron microscopy and nanobeam diffraction

Abstract

As-sputtered and melt-quenched amorphous structures together with the laser-induced crystallized structure of Ge-Sb-Te thin films were investigated using high-resolution electron microscopy (HREM) and nanobeam electron diffraction (NBED). Each of the Ge-Sb-Te thin films was embedded in a four-layered stack, which is the same as the layered structure of phase-change optical disks. Cross-sectional HREM revealed crystalline atomic clusters in the melt-quenched amorphous layer at a greater frequency than in the as-sputtered amorphous layer. Autocorrelation function analysis of the HREM images revealed similarity between the structures of atomic ordered regions in the amorphous phase and that of crystalline Sb. Atomic pair-distribution functions derived from halo NBED intensity analysis indicated that the atomic neighbor correlations developed more in the melt-quenched amorphous phase than in the as-sputtered phase. The development of locally ordered regions is considered to be closely related to the differences in optical properties and crystallization behaviors between these two amorphous phases.