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

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 Ge(2)Sb(2)Te(5) (GST), but not for the equally important class of Sb-Te-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 Ag(3.5)In(3.8)Sb(75.0)Te(17.7) (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.

[1]  T. Ishikawa,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 , 2003 .

[2]  Matthias Wuttig,et al.  Resonant bonding in crystalline phase-change materials. , 2008, Nature materials.

[3]  T. Taguchi,et al.  REX2000: yet another XAFS analysis package , 2005 .

[4]  R. Hoffman Solids and Surfaces: A Chemist's View of Bonding in Extended Structures , 1989 .

[5]  Structure of liquid phase change material AgInSbTe from density functional/molecular dynamics simulations , 2009 .

[6]  John Ziman,et al.  Models of disorder , 1979 .

[7]  M. Wuttig,et al.  Phase-change materials for rewriteable data storage. , 2007, Nature materials.

[8]  K. Binnemans Ionic liquid crystals. , 2005, Chemical reviews.

[9]  R. O. Jones,et al.  Experimentally constrained density-functional calculations of the amorphous structure of the prototypical phase-change material Ge 2 Sb 2 Te 5 , 2009 .

[10]  Hajime Okumura,et al.  Electrical properties of AlGaN∕GaN heterostructures grown on vicinal sapphire (0001) substrates by molecular beam epitaxy , 2006 .

[11]  R. O. Jones,et al.  Structural phase transitions on the nanoscale: The crucial pattern in the phase-change materials Ge2Sb2Te5 and GeTe , 2007 .

[12]  R. O. Jones,et al.  Publisher's Note: Experimentally constrained density-functional calculations of the amorphous structure of the prototypical phase-change material Ge2Sb2Te5 , 2009 .

[13]  Simone Raoux,et al.  Evidence for electronic gap-driven metal-semiconductor transition in phase-change materials , 2009, Proceedings of the National Academy of Sciences.

[14]  R. O. Jones,et al.  Density functional study of amorphous, liquid and crystalline Ge2Sb2Te5: homopolar bonds and/or AB alternation? , 2008, Journal of physics. Condensed matter : an Institute of Physics journal.

[15]  M. Weidemüller,et al.  Imaging Nucleophilic Substitution Dynamics , 2008, Science.

[16]  N. Yamada,et al.  Crystallographic Studies on High-Speed Phase-Change Materials Used for Rewritable Optical Recording Disks , 2004 .

[17]  N. Yamada,et al.  Rapid‐phase transitions of GeTe‐Sb2Te3 pseudobinary amorphous thin films for an optical disk memory , 1991 .

[18]  P. Jóvári,et al.  A new version of the RMC++ Reverse Monte Carlo programme, aimed at investigating the structure of covalent glasses , 2007 .

[19]  Makoto Harigaya,et al.  Structural Analysis of Ag–In–Sb–Te Phase-Change Material , 2002 .

[20]  Noboru Yamada,et al.  Structural basis for the fast phase change of Ge2Sb2Te5: Ring statistics analogy between the crystal and amorphous states , 2006 .

[21]  J L Beeby,et al.  Physics of amorphous materials , 1984 .

[22]  S. Gronert,et al.  Gas phase studies of the competition between substitution and elimination reactions. , 2003, Accounts of chemical research.

[23]  S. G. Bishop,et al.  Observation of the Role of Subcritical Nuclei in Crystallization of a Glassy Solid , 2009, Science.

[24]  N. Yamada,et al.  Electronic structure of amorphous and crystalline ( Ge Te ) 1 − x ( Sb 2 Te 3 ) x investigated using hard x-ray photoemission spectroscopy , 2007 .

[25]  S. Elliott,et al.  Microscopic origin of the fast crystallization ability of Ge-Sb-Te phase-change memory materials. , 2008, Nature materials.

[26]  Noboru Yamada,et al.  Structural study of a Ag 3.4 In 3.7 Sb 76.4 Te 16.5 quadruple compound utilized for phase-change optical disks , 2001 .

[27]  D. A. Shirley,et al.  High-Resolution X-Ray Photoemission Spectrum of the Valence Bands of Gold , 1972 .

[28]  Y. Ohishi,et al.  Structural studies of disordered materials using high-energy x-ray diffraction from ambient to extreme conditions , 2007 .

[29]  Yung-Chiun Her,et al.  Effects of ag and in addition on the optical properties and crystallization kinetics of eutectic Sb70Te30 phase-change recording film , 2003 .

[30]  A. Ankudinov,et al.  REAL-SPACE MULTIPLE-SCATTERING CALCULATION AND INTERPRETATION OF X-RAY-ABSORPTION NEAR-EDGE STRUCTURE , 1998 .

[31]  M. Parrinello,et al.  Coexistence of tetrahedral- and octahedral-like sites in amorphous phase change materials , 2007, 0708.1302.

[32]  J. Robertson,et al.  Bonding origin of optical contrast in phase-change memory materials , 2010 .

[33]  G. Scuseria,et al.  Restoring the density-gradient expansion for exchange in solids and surfaces. , 2007, Physical review letters.

[34]  C. Gan,et al.  Crystallization behavior of Sb70Te30 and Ag3In5Sb60Te32 chalcogenide materials for optical media applications , 2008 .

[35]  T. Ohshima,et al.  Time-Resolved Investigation of Nanosecond Crystal Growth in Rapid-Phase-Change Materials: Correlation with the Recording Speed of Digital Versatile Disc Media , 2008 .

[36]  Martins,et al.  Efficient pseudopotentials for plane-wave calculations. , 1991, Physical review. B, Condensed matter.

[37]  Matthias Wuttig,et al.  Crystallization kinetics of sputter-deposited amorphous AgInSbTe films , 2001 .