Understanding the fast phase-change mechanism of tetrahedrally bonded Cu2GeTe3

Comprehensive analyses of electronic structure and transport phenomena

Keisuke Kobayashi, Jonathan M. Skelton, Yuta Saito, Satoshi Shindo, Masaaki Kobata, Paul Fons, Alexander V. Kolobov, Stephen Elliott, Daisuke Ando, Yuji Sutou

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

Cu2GeTe3 (CGT) phase-change material, a promising candidate for advanced fast nonvolatile random-access-memory devices, has a chalcopyritelike structure with sp3 bonding in the crystalline phase; thus, the phase-change (PC) mechanism is considered to be essentially different from that of the standard PC materials (e.g., Ge-Sb-Te) with threefold to sixfold p-like bonding. In order to reveal the PC mechanism of CGT, the electronic structure change due to PC has been investigated by laboratory hard x-ray photoelectron spectroscopy and combined first-principles density-functional theory molecular-dynamics simulations. The valence-band spectra, in both crystalline and amorphous phases, are well simulated by the calculations. An inherent tendency of Te 5s lone-pair formation and an enhanced participation of Cu 3d orbitals in the bonding are found to play dominant roles in the PC mechanism. The electrical conductivity of as-deposited films and its change during the PC process is investigated in connection with valence-band spectral changes near the Fermi level. The results are successfully analyzed, based on a model proposed by Davis and Mott for chalcogenide amorphous semiconductors. The results suggest that robustness of the defect-band states against thermal stress is a key to the practical application of this material for memory devices.

Original languageEnglish
Article number195105
JournalPhysical Review B
Volume97
Issue number19
Early online date3 May 2018
DOIs
Publication statusPublished - 15 May 2018

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Electronic structure
phase change materials
Phase change materials
electronic structure
Valence bands
Crystalline materials
valence
Amorphous semiconductors
Data storage equipment
amorphous semiconductors
random access memory
spectral bands
Photoelectron spectroscopy
thermal stresses
Fermi level
Thermal stress
x ray spectroscopy
Density functional theory
Molecular dynamics
tendencies

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

Cite this

Understanding the fast phase-change mechanism of tetrahedrally bonded Cu2GeTe3 : Comprehensive analyses of electronic structure and transport phenomena. / Kobayashi, Keisuke; Skelton, Jonathan M.; Saito, Yuta; Shindo, Satoshi; Kobata, Masaaki; Fons, Paul; Kolobov, Alexander V.; Elliott, Stephen; Ando, Daisuke; Sutou, Yuji.

In: Physical Review B, Vol. 97, No. 19, 195105, 15.05.2018.

Research output: Contribution to journalArticle

Kobayashi, K, Skelton, JM, Saito, Y, Shindo, S, Kobata, M, Fons, P, Kolobov, AV, Elliott, S, Ando, D & Sutou, Y 2018, 'Understanding the fast phase-change mechanism of tetrahedrally bonded Cu2GeTe3: Comprehensive analyses of electronic structure and transport phenomena', Physical Review B, vol. 97, no. 19, 195105. https://doi.org/10.1103/PhysRevB.97.195105
Kobayashi, Keisuke ; Skelton, Jonathan M. ; Saito, Yuta ; Shindo, Satoshi ; Kobata, Masaaki ; Fons, Paul ; Kolobov, Alexander V. ; Elliott, Stephen ; Ando, Daisuke ; Sutou, Yuji. / Understanding the fast phase-change mechanism of tetrahedrally bonded Cu2GeTe3 : Comprehensive analyses of electronic structure and transport phenomena. In: Physical Review B. 2018 ; Vol. 97, No. 19.
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