Evaluation of vibrational properties and local structure change during phase transition in Ge2Sb2Te5 and In3SbTe2 phase change materials

Abstract Temperature-dependent local structural details of In 3 SbTe 2 (IST) and Ge 2 Sb 2 Te 5 (GST) phase change materials are explored with the aid of Raman scattering and x-ray photoelectron spectroscopy (XPS) techniques. Significant temperature-induced changes occur in the local structure of the phase change material, facilitating the amorphous to crystalline phase transformation. These two phases exhibit a large resistivity contrast, which is utilized to store data in the phase change memory application. The Raman spectra recorded for IST material suggest that the as-deposited sample (amorphous phase) first crystallized around 300 ∘ C annealing temperature with two binary phases InTe and InSb formations. InTe and InSb phases were obtained at ∼85.5 cm −1 and ∼180 cm −1 Raman shift, respectively, having vibration modes associated with B 1g symmetry and transversal optical phonons with Г 15 symmetry. Further annealing at a higher temperature of 400 ∘ C , a ternary IST phase is obtained at ∼163 cm −1 Raman shift indicating the transformation to a fully crystalline state. On the other hand, the amorphous GST material forms a metastable face-centred cubic phase and stable hexagonal (HEX) phase upon crystallization. The Raman findings demonstrate the changes in vibration modes of Ge–Te and Sb–Te bonds during phase switching without any phase separation. Crystalline GST (HEX phase) comprises rising peaks of GeTe 4 and GeTe 4− n Ge n ( n = 1, 2) corner-sharing tetrahedra with A 1 mode at ∼104.5 cm −1 and ∼137 cm −1 Raman shift, respectively, and a declining Sb 2 Te 3 peak at ∼175 cm −1 , having A 1g (2) vibration mode. Furthermore, the XPS analysis displays the changes in the bonding mechanism of the elements present in the phase change material during the amorphous to crystalline phase transition, firmly supporting the Raman observations.