Morphology and structure of laser-modified Ge2Sb2Te5 films studied by transmission electron microscopy

The morphology and crystal structure of laser-modified areas in an amorphou s Ge2Sb2Te5 him have been investigated by transmission electron microscopy (TEM) and selected area electron diffraction (SAD). Two different types of crystallized areas are found by TEM. Low power laser irradiation leads to c rystallization out of the solid phase. Whereas these crystalline areas are characterized by a fine grained morphology (d(grain) = 5-25 nm), the grain distribution of melt crystallized areas is rather different. It resembles t he well known pattern of solidified alloy ingots but is formed on a differe nt length- and timescale. The crystal structure of both the fine-grained cr ystalline area as well as of the melt-crystallized area is shown to be cubi c and not the more complex hexagonal equilibrium structure of Ge,Sb,Te,. Th ese findings enable a deeper understanding of fast nucleation and growth pr ocesses in phase change media. (C) 2001 Elsevier Science B.V. Ah rights res erved.