Marina Zhezhu, A. Vasilev, M. Sukiasyan, A. Kutuzyan, N. Anosov, M. Yaprintsev, Davit Ghazaryan, and Hermine Gharagulyan | Materials Science and Engineering B | July 28, 2026 | 10.1016/j.mseb.2026.11973110.3390/pr14142337
Abstract
Phase-change Ge–Sb–Te (GST) materials exhibit pronounced optical contrast and tunability driven by structural transformations, enabling a diverse range of photonic and optoelectronic applications. GST materials undergo reversible amorphous–crystalline phase transitions during which the refractive index and extinction coefficient increase significantly in the crystalline phase across a broad spectral range. However, a systematic correlation between local composition, crystalline microstructure, and broadband optical response within as-deposited crystalline GST films has not been established, particularly for films spanning various compositions within a single growth process and in the absence of amorphous-crystalline transitions. Here, we report a systematic study of composition-resolved opto-structural property relationships in as-deposited crystalline GST films spanning Ge3Sb2Te6, Ge2Sb2Te5, and GeSb2Te4 within a single CVD process, avoiding intermediate phase transitions. This enables direct correlations between composition, microstructure, morphology, and broadband optical response across 400–1700 nm. Specifically, the compositional gradient results in a shift of the absorption minimum from ∼815.9 nm to ∼889.8 nm, accompanied by a 5.9-fold change in the intensity, reflecting the strong dependence of optical behavior on composition and microstructure. We further show that femtosecond laser irradiation enables spatially selective tuning of the optical response. Local laser irradiation induces fluence-dependent changes in the optical response across the Vis-NIR range. GeSb2Te4 exhibits the strongest modulation in the NIR range (absorption ratio is 3.2 at 191 J/cm2), Ge2Sb2Te5 shows the highest optical contrast in the Vis range (absorption ratio is 8.1 at 179 J/cm2), whereas Ge3Sb2Te6 exhibits a decrease in absorbance across both spectral ranges. These findings establish crystalline GST films as a platform for broadband-tunable, spatially programmable photonic elements, controllable through both compositional design and localized laser processing.
StellarNet equipment used: BLACK-Comet-SR and DWARF-Star InGaAs-512
How it was used: The two spectrometers provided continuous visible and near-infrared coverage for broadband optical characterization of the composition-gradient films before and after laser treatment.
