Partially Disordered Crystalline State in a Thin GeSbTe Film: Manifestation of Thermally Induced Nanoscale Effect

Using a pulsed electron diffraction instrument, a phase transition in a ~10 nm GeSbTe (GST) film was studied upon heating it from room temperature to ~400°C. During crystallization of a free-standing amorphous sample, the formation of a hexagonal GST phase was detected, for which mixing Sb and Ge leads to a formal violation of translational symmetry and unit cell symmetry. However, upon heating an identical amorphous GST film on a carbon membrane, the crystalline state turned out to be represented only by a cubic phase. Within the framework of the Phillips theory, a qualitative explanation is proposed for such a nanoscale effect in GST, which opens up new possibilities for controlling structural ordering in phase-change memory materials (PCMM).