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Terahertz-infrared spectroscopy of Ge2Sb2Te5 and VO2 films upon temperature-induced phase transitions

Arsenii A. Gavdush (1), Gennadii A. Komandin (1), Kirill I. Zaytsev (1), Dmitry S. Ponomarev (2), Liwen Tan (3), Wanxia Huang (3), Qiwu Shi (3)
1 - Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991, Russia
2 - Institute of Ultra-High Frequency Semiconductor Electronics of the Russian Academy of Sciences, 117105, Moscow, Russia
3 - College of Materials Science and Engineering, Sichuan University, Chengdu, 610065, Sichuan, China


Phase change materials play an important role in modern optics, photonics, microelectronics [1-3]. The phase in such materials can be controlled by various parameters including temperature, electromagnetic field, strain. Most often different phases are associated with the effective refractive index changes. In this study [4] thermally induced phase transitions of Ge2Sb2Te5 (GST) and VO2 thin films were examined. VO2 shows metal–insulator transition accompanied by large changes in conductivity. Transformation from amorphous (a-GST) into cubic (c-GST) and then hexagonal (h-GST) GST phases occurs upon annealing at temperatures of 150 and 300 oC. These phase transitions are accompanied by an abrupt increase in the material conductivity due to increasing of carrier density and mobility. The data on broadband complex dielectric permittivity of GST in different phases are missing until this study, in which a-, c-, and h-GST films on a sapphire substrate were examined using broadband dielectric spectroscopy in the frequency range of 0.06–50 THz. A contribution from the free charge-carriers conductivity and vibrational modes to the broadband response of an analyte is quantified. The broadband electrodynamic response obtained for the three GST phases are important for further research of GST-based devices and technologies.

1. Zilun Gong et al. Phase change materials in photonic devices // Journal of Applied Physics 2021. Vol. 129, P. 030902.
2. Xiaoyang Duan et al. Reconfigurable Multistate Optical Systems Enabled by VO2 Phase Transitions // ACS Photonics 2020. Vol. 7, № 11. P. 2958–2965.
3. Xieyu Chen et al. Reconfigurable and nonvolatile terahertz lithography-free photonic devices based on phase change films // Photonics Research 2023. Vol. 11, № 4. P. 669–681.
4. Arsenii A. Gavdush et al. Terahertz-infrared spectroscopy of Ge2Sb2Te5 films on sapphire: Evolution of broadband electrodynamic response upon phase transitions // Journal of Applied Physics 2023. Vol. 134, P. 085103.

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Arsenii A. Gavdush
Prokhorov General Physics Institute of the Russian Academy of Sciences

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