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Resonant bonding in crystalline phase-change materials

Nature Materials volume 7, pages 653–658 (2008)Cite this article

Abstract

The identification of materials suitable for non-volatile phase-change memory applications is driven by the need to find materials with tailored properties for different technological applications and the desire to understand the scientific basis for their unique properties. Here, we report the observation of a distinctive and characteristic feature of phase-change materials. Measurements of the dielectric function in the energy range from 0.025 to 3 eV reveal that the optical dielectric constant is 70–200% larger for the crystalline than the amorphous phases. This difference is attributed to a significant change in bonding between the two phases. The optical dielectric constant of the amorphous phases is that expected of a covalent semiconductor, whereas that of the crystalline phases is strongly enhanced by resonant bonding effects. The quantification of these is enabled by measurements of the electronic polarizability. As this bonding in the crystalline state is a unique fingerprint for phase-change materials, a simple scheme to identify and characterize potential phase-change materials emerges.

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Figure 1: Sample cross-section.
Figure 2: Infrared reflectance spectra of an AgInTe2 film with a thickness of 0.65 μm.
Figure 3: Infrared reflectance spectra of a Ge2Sb1Te4 film.
Figure 4: Dielectric function ɛ1(ω) and ɛ2(ω) for various materials.
Figure 5: Schematic diagram demonstrating the origin of resonance bonding for Sb.

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Acknowledgements

We gratefully acknowledge the design of Fig. 5 by P. Merkelbach, the careful preparation of phase-change targets by Umicore (Liechtenstein) within the EU project CAMELS and financial support by the Deutsche Forschungsgemeinschaft.

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Authors and Affiliations

  1. Institute of Physics (IA), RWTH Aachen University, 52056 Aachen, Germany

    Kostiantyn Shportko, Stephan Kremers, Michael Woda, Dominic Lencer & Matthias Wuttig

  2. Engineering Department, Cambridge University, Cambridge CB2 1PZ, UK

    John Robertson

  3. JARA-FIT, RWTH Aachen University, 52056 Aachen, Germany

    Matthias Wuttig

Authors
  1. Kostiantyn Shportko
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  2. Stephan Kremers
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  6. Matthias Wuttig
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Correspondence to Matthias Wuttig.

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Shportko, K., Kremers, S., Woda, M. et al. Resonant bonding in crystalline phase-change materials. Nature Mater 7, 653–658 (2008). https://doi.org/10.1038/nmat2226

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