From local structure to nanosecond recrystallization dynamics in AgInSbTe phase-change materials

Journal name:
Nature Materials
Volume:
10,
Pages:
129–134
Year published:
DOI:
doi:10.1038/nmat2931
Received
Accepted
Published online

Abstract

Phase-change optical memories are based on the astonishingly rapid nanosecond-scale crystallization of nanosized amorphous ‘marks’ in a polycrystalline layer. Models of crystallization exist for the commercially used phase-change alloy Ge2Sb2Te5 (GST), but not for the equally important class of SbTe-based alloys. We have combined X-ray diffraction, extended X-ray absorption fine structure and hard X-ray photoelectron spectroscopy experiments with density functional simulations to determine the crystalline and amorphous structures of Ag3.5In3.8Sb75.0Te17.7 (AIST) and how they differ from GST. The structure of amorphous (a-) AIST shows a range of atomic ring sizes, whereas a-GST shows mainly small rings and cavities. The local environment of Sb in both forms of AIST is a distorted 3+3 octahedron. These structures suggest a bond-interchange model, where a sequence of small displacements of Sb atoms accompanied by interchanges of short and long bonds is the origin of the rapid crystallization of a-AIST. It differs profoundly from crystallization in a-GST.

At a glance

Figures

  1. Phase diagram of PC materials and crystallization patterns.
    Figure 1: Phase diagram of PC materials and crystallization patterns.

    a, The most commonly used materials for optical recording are in groups 1 and 2. b, Nucleation-dominated recrystallization (as in GST). c, Growth-dominated recrystallization (AIST).

  2. HXRD data for AIST and GST, and atomic configurations of a-AIST and a-GST.
    Figure 2: HXRD data for AIST and GST, and atomic configurations of a-AIST and a-GST.

    a,b, Structure factors S(Q) and total correlation functions T(r) of AIST and GST (ref. 9). Red line, experimental data of crystalline phase; black line, experimental data of amorphous phase; blue line, DF-RMC model of a-AIST. The DF-RMC and experimental results are practically indistinguishable. c, Section of 640-atom DF-MD model of a-AIST (24 Å×24 Å×12 Å). Ag, silver; In, magenta; Sb, blue; Te, yellow. d, Section of 460-atom DF-MD model of a-GST (24 Å×24 Å×12 Å). Ge, red; Sb, blue; Te, yellow; large cavity, pink.

  3. Valence-band spectra and bond-order distributions in c- and a-AIST.
    Figure 3: Valence-band spectra and bond-order distributions in c- and a-AIST.

    a, Experimental (black) and theoretical (red) valence-band spectra of c-AIST. b, Experimental and theoretical valence-band spectra of a-AIST. Contributions of p-DOS are shown (lower panels) for Sb 5p, Sb 5s, Te 5p, Te 5s and Ag 4d. In 4d (not shown) and Ag 4d peaks in the calculated DOS are shifted by −3.09 eV and −1.25 eV (c-AIST) and −2.96 eV and −1.09 eV (a-AIST) to coincide with the experimental peaks. c,d, Bond-order distributions of Sb–Sb and Sb–Te bonds in a-AIST and c-AIST. Grey shading, crystal; bars, amorphous. See Supplementary Fig. S4.

  4. PC mechanism of a-AIST.
    Figure 4: PC mechanism of a-AIST.

    The bonding electrons are excited by laser light, causing the atoms in the amorphous phase to move. Finally, the central atom with three short (red) and three long (dashed) bonds crosses the centre of the distorted octahedron, interchanging a short and a long bond. Green: resultant vector of short bonds. Resonant bonding between periodic short and long bonds leads to the crystalline A7 network. The grey sticks (lower right) correspond to the red bonds (upper right). Atom colours as in Fig. 2c.

  5. Ring statistics and PC in a-AIST and a-GST.
    Figure 5: Ring statistics and PC in a-AIST and a-GST.

    a, Ring statistics (bond cutoff 3.2 Å) reflect differences in T(r) near 3.0–3.5 Å. b,c, PC scheme in a-AIST and a-GST, respectively. Dashed lines show bonds corresponding to the peak in T(r) near 3.5 Å (Fig. 2b).

References

  1. Meinders, E. R., Mijiritskii, A. V., van Pieterson, L. & Wuttig, M. Optical Data Storage Vol. 4 (Philips Research Book Series, Springer, 2006).
  2. Yamada, N., Ohno, E., Nishiuchi, K., Akahira, N. & Takao, M. Rapid phase transitions of GeTe–Sb2Te3 pseudobinary amorphous thin films for an optical disk memory. J. Appl. Phys. 69, 28492856 (1991).
  3. Matsunaga, T. & Yamada, N. Crystallographic studies on high-speed phase-change materials used for rewritable optical recording disks. Jpn J. Appl. Phys. 43, 47044712 (2004).
  4. Elliott, S. R. Physics of Amorphous Materials (Longman, 1984).
  5. Lee, B-S. et al. Observation of the role of subcritical nuclei in crystallization of a glassy solid. Science 326, 980984 (2009).
  6. Fukuyama, Y. et al. Time-resolved investigation of nanosecond crystal growth in rapid phase-change materials—correlation with the recording speed of digital versatile disc media. Appl. Phys. Exp. 1, 045001 (2008).
  7. Wuttig, M. & Yamada, N. Phase-change materials for rewriteable data storage. Nature Mater. 6, 824832 (2007).
  8. Matsunaga, T., Umetani, Y. & Yamada, N. Structural study of a Ag3.4In3.7Sb76.4Te16.5 quadruple compound utilized for phase-change optical disks. Phys. Rev. B 64, 184116 (2001).
  9. Akola, J. et al. Experimentally constrained density functional calculations of the amorphous structure of the prototypical phase-change material Ge2Sb2Te5 . Phys. Rev. B 80, 020201(R) (2009).
  10. Kohara, S. et al. Structural basis for the fast phase change of Ge2Sb2Te5: Ring statistics analogy between the crystal and amorphous states. Appl. Phys. Lett. 89, 201910 (2006).
  11. Lee, M. L., Shi, L. P., Tian, Y. T., Gan, C. L. & Miao, X. S. Crystallization behavior of Sb70Te30 and Ag3In5Sb60Te32 chalcogenide materials for optical media applications. Phys. Status Solidi a 205, 340344 (2008).
  12. Akola, J. & Jones, R. O. Structural phase transitions on the nanoscale: The crucial pattern in the phase change materials Ge2Sb2Te5 and GeTe. Phys. Rev. B 76, 235201 (2007).
  13. Akola, J. & Jones, R. O. Density functional study of amorphous, liquid, and crystalline Ge2Sb2Te5: Homopolar bonds and/or AB alternation? J. Phys. Condens. Matter 20, 365103 (2008).
  14. Tashiro, H. et al. Structural analysis of Ag–In–Sb–Te phase-change material. Jpn J. Appl. Phys. 41, 37583759 (2002).
  15. Kim, J-J. et al. Electronic structure of amorphous and crystalline (GeTe)1−x(Sb2Te3)x investigated using hard X-ray photoemission spectroscopy. Phys. Rev. B 76, 115124 (2007).
  16. Hoffmann, R. Solids and Surfaces: A Chemist’s View of Bonding in Extended Structures (Wiley-VCH, 1989).
  17. Shportko, K. et al. Resonant bonding in crystalline phase-change materials. Nature Mater. 7, 653658 (2008).
  18. Huang, B. & Robertson, J. Bonding origin of optical contrast in phase-change memory materials. Phys. Rev. B 81, 081204 (2010).
  19. Gronert, S. Gas phase studies of the competition between substitution and elimination reactions. Acc. Chem. Res. 36, 848857 (2003).
  20. Mikosch, J. et al. Imaging nucleophilic substitution dynamics. Science 319, 183186 (2008).
  21. Binnemans, K. Ionic liquid crystals. Chem. Rev. 105, 41484204 (2005).
  22. Njoroge, W. K. & Wuttig, M. Crystallization kinetics of sputter-deposited amorphous AgInSbTe films. J. Appl. Phys. 90, 38163821 (2001).
  23. Shakhvorostov, D. et al. Evidence of electronic gap-driven metal–semiconductor transition in phase change materials. Proc. Natl Acad. Sci. USA 106, 1090710911 (2009).
  24. Cooper, A. R. Zachariasen’s rules, Madelung constant, and network topology. Phys. Chem. Glasses 19, 6068 (1978).
  25. Ziman, J. M. Models of Disorder (Cambridge Univ. Press, 1979).
  26. Her, U-C., Chen, H. & Hsu, Y-S. Effects of Ag and In addition on the optical properties and crystallization kinetics of eutectic Sb70Te30 phase-change recording film. J. Appl. Phys. 93, 1009710103 (2003).
  27. Caravati, S., Bernasconi, M., Kühne, T. D., Krack, M. & Parrinello, M. Coexistence of tetrahedral- and octahedral-like sites in amorphous phase change materials. Appl. Phys. Lett. 89, 171906 (2007).
  28. Hegedüs, J. & Elliott, S. R. Microscopic origin of the fast crystallization ability of Ge–Sb–Te phase-change memory materials. Nature Mater. 7, 399405 (2008).
  29. Kohara, S. et al. Structural studies of disordered materials using high-energy X-ray diffraction from ambient to extreme conditions. J. Phys. Condens. Matter 19, 506101 (2007).
  30. Ankudinov, A. L., Ravel, B., Rehr, J. J. & Conradson, S. D. Real-space multiple-scattering calculation and interpretation of X-ray-absorption near-edge structure. Phys. Rev. B 58, 75657576 (1998).
  31. Taguchi, T., Ozawa, T. & Yashiro, H. REX2000: Yet another XAFS analysis package. Phys. Scr. T115, 205206 (2005).
  32. Kobayashi, K. et al. High resolution–high energy X-ray photoelectron spectroscopy using third-generation synchrotron radiation source, and its application to Si–high k insulator systems. Appl. Phys. Lett. 83, 10051007 (2003).
  33. Shirley, D. A. High-resolution X-ray photoemission spectrum of the valence bands of gold. Phys. Rev. B 5, 47094714 (1972).
  34. CPMD version 3.13. © IBM Corporation (1990–2009), © MPI für Festkörperforschung, Stuttgart (1997–2001).
  35. Perdew, J. P. et al. Restoring the density-gradient expansion for exchange in solids and surfaces. Phys. Rev. Lett. 100, 136406 (2008).
  36. Troullier, N. & Martins, J. L. Efficient pseudopotentials for plane-wave calculations. Phys. Rev. B 43, 19932006 (1991).
  37. Akola, J. & Jones, R. O. Structure of liquid phase change material AgInSbTe from density functional/molecular dynamics simulations. Appl. Phys. Lett. 94, 251905 (2009).
  38. Greben, O., Jóvári, P., Temleitner, L. & Pusztai, L. A new version of the RMC++ reverse Monte Carlo programme, aimed at investigating the structure of covalent glasses. J. Optoelectron. Adv. Mater. 9, 30213027 (2007).

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Author information

Affiliations

  1. Panasonic Corporation, 3-1-1 Yagumo-Nakamachi, Moriguchi, Osaka 570-8501, Japan

    • Toshiyuki Matsunaga,
    • Noboru Yamada &
    • Rie Kojima
  2. JST, CREST, 5 Sanbancho, Chiyoda-ku, Tokyo 102-0075, Japan

    • Toshiyuki Matsunaga,
    • Shinji Kohara,
    • Noboru Yamada &
    • Masaki Takata
  3. Institut für Festkörperforschung, Forschungszentrum Jülich, D-52425 Jülich, Germany

    • Jaakko Akola &
    • Robert O. Jones
  4. Nanoscience Center, Department of Physics, University of Jyväskylä, PO Box 35, FI-40014 Jyväskylä, Finland

    • Jaakko Akola
  5. Department of Physics, Tampere University of Technology, PO Box 692, FI-33101 Tampere, Finland

    • Jaakko Akola
  6. Japan Synchrotron Radiation Research Institute/SPring-8, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan

    • Shinji Kohara,
    • Tetsuo Honma,
    • Eiji Ikenaga &
    • Masaki Takata
  7. Beamline Station at SPring-8, National Institute for Materials Science, 1-1-1 Kouto, Sayo-gun, Hyogo 679-5198, Japan

    • Keisuke Kobayashi
  8. German Research School for Simulation Sciences, FZ Jülich and RWTH Aachen University, D-52425 Jülich, Germany

    • Robert O. Jones
  9. RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan

    • Masaki Takata
  10. Department of Advanced Materials, University of Tokyo, Chiba 277-8561, Japan

    • Masaki Takata

Contributions

The experiments/calculations were carried out and analysed as follows: sample preparation, R.K., T.M., N.Y.; high-energy XRD and RMC, S.K., M.T.; EXAFS, T.H., S.K., T.M.; XPS, E.I., K.K., T.M.; DF-MD, J.A., R.O.J. The manuscript was planned by J.A., R.O.J., S.K., T.M. and N.Y. and written by R.O.J.

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The authors declare no competing financial interests.

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