Overcoming the Thermal Stability Limit of Chalcogenide Phase‐Change Materials for High‐Temperature Applications in GeSe1‐xTex Thin Films

The electrical, optical, and structural properties of GeSe1-xTex phase-change materials thin films with 0.16 <= x <= 1 prepared by cosputtering of GeSe and GeTe targets are studied. The crystallization temperature of the films increases significantly when the Te content decreases. Se-rich films show an extremely large electrical contrast between their amorphous and crystalline states. A high polarizability of the crystalline phase is observed in the entire x range and is related to the presence of metavalent bonds. This is explained by the persistence of a rhombohedral crystalline phase, isostructural to GeTe, in the GeSe1-xTex films down to x = 0.16. Hence, the substitution of only 16 at% of the Se atoms by Te atoms transforms the covalent GeSe into a phase-change material with a huge and unprecedented contrast of resistivity (up to 11 orders of magnitude) and a very high thermal stability (up to 10 years at 272 degrees C) for an alloy exhibiting no phase separation upon crystallization. This outstanding combination of properties makes Se-rich GeSe1-xTex thin films extremely promising for integration in memory devices requiring a very high data retention such as automotive and embedded applications.