Vacancy Structures and Melting Behavior in Rock-Salt GeSbTe

Zhang, Bin; Wang, Xue Peng; Shen, Zhen; Li, Xian Bin; Wang, Chuan Shou; Chen, Yong Jin; Li, Ji Xue; Zhang, Jinxing; Zhang, Ze; Zhang, Shou-Cheng; Han, Xiao

doi:10.1038/srep25453

Cited by 52 publications

(44 citation statements)

References 49 publications

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“…For such models, the electronic states near the Fermi level become fully extended [12,15]. Cubic GST samples with ordered “vacancy layers” have been produced experimentally very recently [93,94,95] and measured to be metallic [93,96], which confirms the DFT predictions in Ref. [15].…”

Section: Discussionsupporting

confidence: 62%

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A Review on Disorder-Driven Metal–Insulator Transition in Crystalline Vacancy-Rich GeSbTe Phase-Change Materials

Wang

Mazzarello

et al. 2017

Materials

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Metal–insulator transition (MIT) is one of the most essential topics in condensed matter physics and materials science. The accompanied drastic change in electrical resistance can be exploited in electronic devices, such as data storage and memory technology. It is generally accepted that the underlying mechanism of most MITs is an interplay of electron correlation effects (Mott type) and disorder effects (Anderson type), and to disentangle the two effects is difficult. Recent progress on the crystalline Ge1Sb2Te4 (GST) compound provides compelling evidence for a disorder-driven MIT. In this work, we discuss the presence of strong disorder in GST, and elucidate its effects on electron localization and transport properties. We also show how the degree of disorder in GST can be reduced via thermal annealing, triggering a disorder-driven metal–insulator transition. The resistance switching by disorder tuning in crystalline GST may enable novel multilevel data storage devices.

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Section: Discussionsupporting

confidence: 62%

“…Such small energy difference suggests that this ordered cubic phase might be produced experimentally. Very recently, several groups reported the existence of ordered cubic GST in experiments, which were obtained by molecular beam epitaxy (MBE) [93], pulsed laser deposition [94,95], or by the application of a designed electric current [96]. …”

Section: Discussionmentioning

confidence: 99%

A Review on Disorder-Driven Metal–Insulator Transition in Crystalline Vacancy-Rich GeSbTe Phase-Change Materials

Wang

Mazzarello

et al. 2017

Materials

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“…The vacancy ordering process in the rocksalt phase occurs at the {111} planes 25, 26 . In a single grain these planes form a tetrahedral.…”

Section: Resultsmentioning

confidence: 99%

Role of interfaces on the stability and electrical properties of Ge2Sb2Te5 crystalline structures

Mio

Privitera

Bragaglia

et al. 2017

Sci Rep

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GeSbTe-based materials exhibit multiple crystalline phases, from disordered rocksalt, to rocksalt with ordered vacancy layers, and to the stable trigonal phase. In this paper we investigate the role of the interfaces on the structural and electrical properties of Ge2Sb2Te5. We find that the site of nucleation of the metastable rocksalt phase is crucial in determining the evolution towards vacancy ordering and the stable phase. By properly choosing the substrate and the capping layers, nucleation sites engineering can be obtained, thus promoting or preventing the vacancy ordering in the rocksalt structure or the conversion into the trigonal phase. The vacancy ordering occurs at lower annealing temperatures (170 °C) for films deposited in the amorphous phase on silicon (111), compared to the case of SiO2 substrate (200 °C), or in presence of a capping layer (330 °C). The mechanisms governing the nucleation have been explained in terms of interfacial energies. Resistance variations of about one order of magnitude have been measured upon transition from the disordered to the ordered rocksalt structure and then to the trigonal phase. The possibility to control the formation of the crystalline phases characterized by marked resistivity contrast is of fundamental relevance for the development of multilevel phase change data storage.

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“…Such swift expansion of the big h-grain was usually named as the “growth-dominated crystallization” for f-to-h transition of GST 16, 21 , no matter what crystallographic configurations the small grains would have. We also speculate that the vacancy-ordering process into {111} planes 11, 12, 17 may or may not occur in every f-grain, or to say, it is not an indispensable way for f-grains evolving into h-ones especially in the growth period. The adjustments by sliding the building blocks between similar f- and h-atomic configurations 17, 19, 21 would be more likely to involve the incubation of h-seeds from the f-matrix.…”

Section: Introductionmentioning

confidence: 95%

“…Recently, an intermediate state of f-GST, namely vacancy-ordering cubic (VOC) phase, was theoretically 17 and experimentally 11, 12 demonstrated to play a key role during the f-to-h transition. Once 100% vacancy-aggregation into {111} planes achieves and forms non-atomic layers in f-GST resembling the Van der Waals interaction gaps in h-GST, the system energy is as small as the equilibrium h-phase 17 .…”

Section: Introductionmentioning

confidence: 99%

Surface Energy Driven Cubic-to-Hexagonal Grain Growth of Ge2Sb2Te5 Thin Film

Zheng

Cheng

et al. 2017

Sci Rep

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Phase change memory (PCM) is a promising nonvolatile memory to reform current commercial computing system. Inhibiting face-centered cubic (f-) to hexagonal (h-) phase transition of Ge2Sb2Te5 (GST) thin film is essential for realizing high-density, high-speed, and low-power PCM. Although the atomic configurations of f- and h-lattices of GST alloy and the transition mechanisms have been extensively studied, the real transition process should be more complex than previous explanations, e.g. vacancy-ordering model for f-to-h transition. In this study, dynamic crystallization procedure of GST thin film was directly characterized by in situ heating transmission electron microscopy. We reveal that the equilibrium to h-phase is more like an abnormal grain growth process driven by surface energy anisotropy. More specifically, [0001]-oriented h-grains with the lowest surface energy grow much faster by consuming surrounding small grains, no matter what the crystallographic reconfigurations would be on the frontier grain-growth boundaries. We argue the widely accepted vacancy-ordering mechanism may not be indispensable for the large-scale f-to-h grain growth procedure. The real-time observations in this work contribute to a more comprehensive understanding of the crystallization behavior of GST thin film and can be essential for guiding its optimization to achieve high-performance PCM applications.

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Vacancy Structures and Melting Behavior in Rock-Salt GeSbTe

Cited by 52 publications

References 49 publications

A Review on Disorder-Driven Metal–Insulator Transition in Crystalline Vacancy-Rich GeSbTe Phase-Change Materials

A Review on Disorder-Driven Metal–Insulator Transition in Crystalline Vacancy-Rich GeSbTe Phase-Change Materials

Role of interfaces on the stability and electrical properties of Ge2Sb2Te5 crystalline structures

Surface Energy Driven Cubic-to-Hexagonal Grain Growth of Ge2Sb2Te5 Thin Film

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