Phase-change recording materials with a growth-dominated crystallization mechanism: A materials overview

Pieterson, L. van; Lankhorst, Marc M.; Schijndel, M. van; Kuiper, A. E. T.; Roosen, Joris

doi:10.1063/1.1868860

Cited by 235 publications

(168 citation statements)

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“…Second, the crystallization velocity in GeSb is very high (8). This-in addition to the isothermal means of reaching the amorphous state being simpler-significantly reduces the demand on computational resources (12,14) required to track the process by using ab initio MD (AIMD) and to test the MD results against our experimental data.…”

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confidence: 99%

“…The difficulty in following the causal linkage between electronic and atomistic configurations during the phase transition (6, 7) lies in part in the short time scales of the process (4,8), in part, in the nonequilibrium (nonergodic) nature of the glassy amorphous states (9), and, in part, in the global nature of the usual experimental techniques, such as charge transport or optical reflectivity (3). Electronic driving mechanisms for the phase-change considered early on (2, 10) were never satisfactorily proved (11), whereas numerous ab initio molecular dynamics (MD) studies (12)(13)(14)(15) tended to emphasize local atomic rearrangements (16) while sidelining the relationship to electronic structure.…”

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confidence: 99%

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Evidence for electronic gap-driven metal-semiconductor transition in phase-change materials

Shakhvorostov

Nistor

Krusin‐Elbaum

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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Phase-change materials are functionally important materials that can be thermally interconverted between metallic (crystalline) and semiconducting (amorphous) phases on a very short time scale.Although the interconversion appears to involve a change in local atomic coordination numbers, the electronic basis for this process is still unclear. Here, we demonstrate that in a nearly vacancy-free binary GeSb system where we can drive the phase change both thermally and, as we discover, by pressure, the transformation into the amorphous phase is electronic in origin. Correlations between conductivity, total system energy, and local atomic coordination revealed by experiments and long time ab initio simulations show that the structural reorganization into the amorphous state is driven by opening of an energy gap in the electronic density of states. The electronic driving force behind the phase change has the potential to change the interconversion paradigm in this material class.ab initio simulations ͉ structural phase change ͉ electronic phase transitions ͉ ac conductivity

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confidence: 99%

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confidence: 99%

Evidence for electronic gap-driven metal-semiconductor transition in phase-change materials

Shakhvorostov

Nistor

Krusin‐Elbaum

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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“…10 The latter is the time-limiting step in the write-erase cycle, and there is growing interest in alloys of Ge and/or Ga with Sb and Te. We study here Ga 11 Ge 11 Te 78 (GGT), a Te-rich alloy containing equal parts of Ga and Ge.…”

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confidence: 99%

Structure, electronic, and vibrational properties of glassy Ga11Ge11Te78: Experimentally constrained densi

et al. 2012

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The atomic structure and electronic and vibrational properties of glassy Ga 11 Ge 11 Te 78 have been studied by combining density functional (DF) simulations with x-ray (XRD) and neutron diffraction (ND), extended x-ray absorption fine structure (EXAFS), and Raman spectroscopies. The final DF structure (540 atoms) was refined using reverse Monte Carlo methods to reproduce the XRD and ND data as well as Ge and Ga K-edge EXAFS spectra, while maintaining a semiconducting band gap and a total energy close to the DF minimum. The local coordination of Ga is tetrahedral, while Ge has twice as many tetrahedral as defective octahedral configurations. The average coordination numbers are Ga, 4.1, Ge, 3.8, and Te, 2.6. The chemical bonding around Ga involves Ga 4s, Ga 4p, Te 5s, and Te 5p orbitals, and the bond strengths show bonding close to covalent, as in Ge. There are fewer Te chains and cavities than in amorphous Te, and a prepeak in the structure factor at 1.0Å −1 indicates medium-range order of the Ga/Ge network. Density functional calculations show that contributions of Te-Te, Ga-Te, and Ge-Te bonds dominate the experimental Raman spectra in the 110-150 cm −1 range.

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“…Sb 8 Te 2 materials have been identified as having growth dominated crystallization. 12 Figure 1 shows that the crystallization time for this material is reduced by an order of magnitude through the addition of Bi. The rate of crystal growth is dependent on activation energy for crystallization; 13 however, from the measurements reported here, the activation energy is only marginally reduced by addition of Bi.…”

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Reduction in crystallization time of Sb:Te films through addition of Bi

Simpson

Hewak

Fons³

et al. 2008

Applied Physics Letters

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The electrical, optical, and phase change properties of bismuth doped Sb 8 Te 2 films have been characterized. Thin films of the material, with up to 15 at. % percent Bi, have been synthesized; amorphous films were stable at room temperature with a Bi concentration of up to 13 at. %. The effect of Bi on the phase change properties of the film is shown to reduce the crystallization time by an order of magnitude while the crystallization activation energy reduction is minimal; 0.2 eV. Over the last 30 years, 1 phase change materials have been extensively investigated for optical data storage applications. Phase change recording is based on the reversible switching between the crystalline and amorphous states. The rate that data can be erased and directly overwritten is reliant on the crystallization time of the material; thus, understanding the effect of compositional variations on the crystallization times of these materials is of key importance.The effect of Bi doping, in the well researched Ge 2 Sb 2 Te 5 ͑GST͒ phase change alloy, has been reported by a number of groups. [2][3][4] Experimental results demonstrate that the use of Bi as a dopant could play an important role in the demonstration of improved data storage materials. When doped in GST, Bi is known to reduce the transition temperatures without affecting the crystal structure or its lattice parameters. 2In addition to the well known GST composition, the Sb:Te binary compositions are also known phase change materials. 5The appreciation of bismuth's mechanism in Sb:Te compounds could aid the understanding in the somewhat more complex Bi doped ternary systems. The Sb 2 Te phase shows a wide compositional tolerance with Sb content ranging from 63 to 81 at. %. 6 In this work, samples containing 80% Sb have been doped with Bi; close to the maximum Sb concentration at which the Sb 2 Te phase is formed. Since this crystal can form over a wide Sb compositional range, it is anticipated that it will show some acceptance of the Bi atom. The crystallization, optical, and electrical properties have been investigated.The Bi content was varied between 0 and 15 at. % by attaching pure Bi pieces to a Sb 8 Te 2 sputtering target. Sputtering was performed in an argon atmosphere, controlled at 0.5 Pa, with a rf power of 100 W. Films, with thickness of 100 nm, were deposited onto Si and SiO 2 substrates. The film composition was measured by x-ray fluorescence spectroscopy using a Rigaku RIX 2100 system. The crystallization temperature and its activation energy were measured by monitoring the reflection as a function of temperature, using a Linkam microscope furnace in conjunction with a broad visible source and a monochromator-detector setup. Measurements of the crystallization temperature were made at heating rates of 5, 10, 15, 20, and 25°C min −1 in an Ar atmosphere. These heating rates are many orders of magnitude lower than that of laser or joule heating. However, for the purpose of comparing samples measured in the same fashion, these heating rates were deemed suffici...

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Phase-change recording materials with a growth-dominated crystallization mechanism: A materials overview

Cited by 235 publications

References 13 publications

Evidence for electronic gap-driven metal-semiconductor transition in phase-change materials

Evidence for electronic gap-driven metal-semiconductor transition in phase-change materials

Structure, electronic, and vibrational properties of glassy Ga11Ge11Te78: Experimentally constrained densi

Reduction in crystallization time of Sb:Te films through addition of Bi

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