Optical constants acquisition and phase change properties of Ge₂Sb₂Te₅ thin films based on spectroscopy

Abstract

In this work, phase change chalcogenide Ge 2 Sb 2 Te 5 (GST) thin films were fabricated by magnetron sputtering. The optical properties, especially the optical constants (refractive index and extinction coefficient), of such alloys were systematically studied by investigating their thermally and photo-

Ge-Sb-Te Chalcogenide Thin Films Deposited by Nanosecond, Picosecond, and Femtosecond Laser Ablation

“…In our case, the spectra recorded for this type of material are described by two peaks: 110 and 163 cm −1 . In accordance with the data published in References [6,36,37], the first peak was attributed to the active Raman E g mode, while the second one to the A 1g vibrational mode. However, for the Sb 2 Te 3 film deposited using the 266 nm radiation of the Nd-YAG laser, additional vibrational modes were detected which were associated with the antimony-rich phase observed through XRD measurements.…”

“…The good agreement of their observations to the experimental vibrational spectra allowed them to assign each peak to specific phonons: E g at 46 and 113 cm −1 and A 1g at 62 and 166 cm −1 . A sketch of the displacement patterns of phonons is also presented in Reference [37]. Two peaks at 110 and 165 cm −1 were also observed by Nemec et al [6] in the Raman spectroscopy study on Sb 2 Te 3 bulk materials used as targets in the deposition process.…”

Notes on Reproducibility of Ge2Sb2Te5 Properties

“…At the outset, it may be reasonable to assume that the annealing temperature governs film structures leading to different conductivities. However, X‐ray patterns of the present films, exemplified in Figure , substantiated that the crystallite size evaluated by applying Scherrer's equation to the 200 peak (at 2 θ ≈ 30°) was ≈15 nm, irrespective of the annealing temperatures of 200 and 250 °C (with a heating rate of 5−10 °C min −1 and a holding duration of 10 min in Ar atmosphere), the behavior being similar to that reported in previous studies . Nevertheless, since the amorphous structure provides broad low‐intensity halos, it is plausible that noncrystalline regions and/or grain boundaries still remain, which affect the scattered conductivities.…”

“…The cubic and hexagonal phases are obtained by annealing at 185 and 300 °C, respectively, for 10 min in Ar gas atmosphere. The peak indices follow previous studies …”

“…These new applications use multilevel operations with subtle optical or electrical changes, whereas what is surprising is that related fundamental properties have scarcely been reproduced. For instance, in contrast to more‐or‐less fixed optical‐gap energies of 0.7–0.9 eV in amorphous films, refractive indices reported so far scatter over 3.3–4.5 (at λ ≈ 1–2 μm) and electrical conductivities at room temperatures extend over two orders of magnitude (see Figure ).…”