Ge–Sb–Te thin films deposited by pulsed laser: An ellipsometry and Raman scattering spectroscopy study

Abstract

Pulsed laser (532 nm) deposited Ge2Sb2Te5 thin films were investigated by means of spectroscopic ellipsometry and Raman scattering spectroscopy. Tauc–Lorentz and Cody–Lorentz models were employed for the evaluation of optical functions of thin films in as-deposited (amorphous) and crystalline (cubic) phases. The models’ parameters (Lorentz oscillator amplitude, resonance energy, oscillator width, optical band gap, and Urbach energy) calculated for amorphous and crystalline states are discussed. The vibrational modes observed in Raman spectra of amorphous layers are attributed to GeTe4−nGen (n=1, 2, eventually 0) tetrahedra connected by corners (partly by edges) and SbTe3 units. The Raman spectra of crystalline thin films suggest that the local bonding arrangement around Ge atoms changes; GeTe component is thus mainly responsible for the phase transition in Ge2Sb2Te5 alloys.

Nanoscale mechanically induced structural and electrical changes in Ge2Sb2Te5 films

“…4,6 Similar differences in the Raman spectra between unmodified and modified areas were observed on 70 nm and 2000 nm thick Ge 2 Sb 2 Te 5 films. Moreover, the Raman spectrum obtained on the modified area after exposure to the higher laser intensity, also shown in Fig.…”

“…Despite the long-established technological applications of chalcogenide films in optical data storage devices and the high level reached in the development of PCRAM, the phase change process of such compounds is still the object of intense theoretical and experimental investigations. These include the study of the atomic bonds rearrangement upon phase transition, using, e.g., Raman scattering spectroscopy measurements, which are very sensitive to the lattice vibrations that reflect the local symmetry of the material, [3][4][5][6] and the investigation on the structural changes induced by hydrostatic pressure. 7,8 On the other hand, alternative processes for the writing and reading of information that would allow higher storage density and overcome, for instance, the limits imposed by diffraction of laser impulse in optical storage devices are sought.…”

Optically reconfigurable metasurfaces and photonic devices based on phase change materials

“…This allows on-demand writing of dielectric metamaterial patterns with resonances at near-infrared frequencies where the available spatial resolution is sufficient to write non-diffracting two-dimensional arrays of sub-wavelength meta-molecules. Moreover, in the spectral range between 2 and 2.2 microns amorphous GST has absorption less than 0.3 µm -1 which is important to achieve high-quality resonances 35 . We demonstrate a dipolar dielectric metamaterial, a two-dimensional array of rectangular crystalline inclusions in the amorphous film (seen in Fig.…”

Pulsed laser deposited amorphous chalcogenide and alumino-silicate thin films and their multilayered structures for photonic applications

“…We already reported pulsed laser deposition (PLD) as a thin films fabrication technique viable for the amorphous chalcogenides as well as alumino-silicates being advantageous due to its simplicity, easy control of the process, often stoichiometric transfer of target material to the films, and possibility to fabricate multilayered structures [17][18][19][20]. However, the PLD has a drawback (compared to other deposition techniques such as thermal evaporation) of more difficult control in terms of deposition rate reproducibility; on the other hand it has the advantage of depositing luminescent layers.…”