Amorphous and crystallized Ge–Sb–Te thin films deposited by pulsed laser: Local structure using Raman scattering spectroscopy

UV pulsed laser deposition was employed for the fabrication of amorphous (GeTe)x(Sb2Te3)1−x, (x = 1, 0.66, 0.5, 0.33, and 0) thin films. The local structure of as-deposited (amorphous) as well as annealed (crystallized) layers was studied using Raman scattering spectroscopy. Raman spectra were recorded on bulk materials used for the deposition as well. The vibrational modes observed in amorphous Ge–Sb–Te films are attributed, apart from defective octahedral coordination, to GeTe4−nGen (n = 1, 2, eventually 0) corner- and/or edge-sharing tetrahedra and SbTe3 pyramidal entities, the latter dominated Raman spectra of all the films containing Sb2Te3. The structure of crystallized GeTe and Sb2Te3 resembled that of starting bulk materials which is evidenced by the presence of Γ3 (E) and Γ1 (A1) modes of rhombohedrally deformed rocksalt GeTe and Eg (2) and A1g (2) modes of hexagonal Sb2Te3. We propose that in case of crystallized Ge2Sb2Te5, Ge1Sb2Te4, and Ge1Sb4Te7 films, Raman active features might be attributed to defective octahedral local structure and/or softened A1 mode of corner-sharing GeTe4 tetrahedra, A1 mode of corner-sharing GeTe4−nGen (n = 1, 2) tetrahedra, GeTe4 F2 mode, Sb–Te mode in SbTe3 entities, eventually Eg (2) and A1g (2) modes of hexagonal Sb2Te3.