Evidence for segregation of Te in Ge2 Sb2 Te5 films: Effect on the "phase-change" stress

Abstract

The authors present direct evidence for Te segregation to the grain boundaries in chalcogenide Ge2 Sb2 Te5 films by using transmission electron microscopy scans with a 0.5 nm diameter focused probe. This finding is consistent with the observed impeded grain growth and with the post-transition relief of a "spikelike" stress, fully to the pretransition level. Te motion shows up in void formation below 200 °C, a pileup of Te at the surface and its loss at higher (above 400 °C) temperatures. Tuning the driving force for this segregation may be key for the optimal phase-change material design. © 2007 American Institute of Physics.