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 language | English |
|---|---|
| Article number | 195105 |
| Journal | Physical Review B |
| Volume | 97 |
| Issue number | 19 |
| Early online date | 3 May 2018 |
| DOIs | |
| Publication status | Published - 15 May 2018 |
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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 journal › Article
}
TY - JOUR
T1 - Understanding the fast phase-change mechanism of tetrahedrally bonded Cu2GeTe3
T2 - Comprehensive analyses of electronic structure and transport phenomena
AU - Kobayashi, Keisuke
AU - Skelton, Jonathan M.
AU - Saito, Yuta
AU - Shindo, Satoshi
AU - Kobata, Masaaki
AU - Fons, Paul
AU - Kolobov, Alexander V.
AU - Elliott, Stephen
AU - Ando, Daisuke
AU - Sutou, Yuji
PY - 2018/5/15
Y1 - 2018/5/15
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=85047015626&partnerID=8YFLogxK
U2 - 10.1103/PhysRevB.97.195105
DO - 10.1103/PhysRevB.97.195105
M3 - Article
VL - 97
JO - Physical Review B : Condensed Matter and Materials Physics
JF - Physical Review B : Condensed Matter and Materials Physics
SN - 1098-0121
IS - 19
M1 - 195105
ER -