Molecular dynamics study on the formation of dipole layer at high-<i>k</i>/SiO<sub>2</sub>interfaces

Kuriyama, Ryo; Hashiguchi, Masahiro; Takahashi, Ryusuke; Shimura, Kosuke; Ogura, Atsushi; Satoh, S.; Watanabe, Takanobu

doi:10.7567/jjap.53.08lb02

Cited by 11 publications

(13 citation statements)

References 26 publications

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“…The atomistic picture of the oxygen density difference accommodation model was successfully reproduced in our previous molecular dynamics (MD) simulation 18) for the Al 2 O 3 =SiO 2 system. In this simulation, there was a preferential migration of O − ions from the Al 2 O 3 side to the SiO 2 side, resulting in the formation of a built-in potential of ∼0.5 eV at the Al 2 O 3 =SiO 2 interface.…”

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confidence: 86%

“…In a previous study, 18,31) an imbalance of multipole potentials between the two oxide layers was proposed as the origin of the O − -ion migration. SiO 2 is composed of a covalent network of SiO 4 tetrahedra that have an octupole moment around the Si ion.…”

mentioning

confidence: 99%

“…According to the series of MD simulations presented thus far, O − -ion migration across the Al 2 O 3 =SiO 2 interface occurred immediately after the attachment of the Al 2 O 3 and SiO 2 surfaces. 18,31) Because an apparently systematic interatomic force acting in the direction of the SiO 2 side was applied on the O − ions in the Al 2 O 3 surface, this mechanism differs from the ordinary diffusion process caused by the density gradient. In our MD simulation, the entropic effect was not the dominant origin of the O − -ion migration.…”

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confidence: 99%

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Driving force of oxygen-ion migration across high-k/SiO₂ interface

Kunugi

Nakagawa

Watanabe

2017

Appl. Phys. Express

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We clarified the mechanism of oxygen (O−)-ion migration at a high-k/SiO2 interface, which is a possible origin of the flat-band voltage shift in metal/high-k gate stacks. The oxygen density difference accommodation model was reproduced by a molecular dynamics simulation of an Al2O3/SiO2 structure, in which O− ions migrate from the higher oxygen density side to the lower one. We determined that the driving force of the O−-ion migration is the short-range repulsion between ionic cores. The repulsive force is greater in materials with a higher oxygen density, pushing O− ions to the lower oxygen density side.

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confidence: 99%

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confidence: 99%

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Driving force of oxygen-ion migration across high-k/SiO₂ interface

Kunugi

Nakagawa

Watanabe

2017

Appl. Phys. Express

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“…For example, the XYZ crystal can be understood as stuffing the (YZ) nzinc-blende sublattice with an X n+ ion. 22 and ScPtSb with 18 valence electrons is found to be a narrow gap semiconductor with E g = 0.7 eV. 23 The electron count is illustrated in Figure 1c.…”

Section: Half-heuslers: Crystal Structure and Electronic Structurementioning

confidence: 99%

Half-Heusler topological insulators

Yan

Visser

2014

MRS Bull.

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We predict the existence of triple point fermions in the band structure of several half-Heusler topological insulators by ab initio calculations and the Kane model. We find that many half-Heusler compounds exhibit multiple triple points along four independent C3 axes, through which the doubly degenerate conduction bands and the nondegenerate valence band cross each other linearly nearby the Fermi energy. When projected from the bulk to the (111) surface, most of these triple points are located far away from the surface ¯ Γ point, as distinct from previously reported triple point fermion candidates. These isolated triple points give rise to Fermi arcs on the surface, that can be readily detected by photoemission spectroscopy or scanning tunneling spectroscopy. The discovery of topological insulators (TIs) [1, 2] has generated much interest in the search for other novel topological states in condensed matter physics and materials science. As quasiparticle analogues of elementary particles of the standard model, Dirac fermions [3-6] and Weyl fermions [7-14] have recently been found in several materials (see reviews Refs. 15 and 16). Both Dirac and Weyl fermions exhibit Fermi arcs, unclosed Fermi surfaces, on the boundary, as a hallmark for the experimental detection. More recently, several exotic types of fermions, which do not have elementary particle counterparts, have been theoretically predicted as quasiparticle excitations near certain band crossing points that are protected by specific space-group symmetries [17, 18]. In particular, triple point (TP) fermions have been predicted in many materials with triply degenerate band crossing points [19-25]. These predictions have stimulated intensive experimental studies to search for their signatures, for example, using angle-resolved photoemission spectroscopy (ARPES) [26] and transport properties [27]. TPs can be viewed as an intermediate phase between fourfold degenerate Dirac points and twofold degenerate Weyl points. They also give rise to Fermi arcs when projected onto certain specific crystal facets. However, the detection of TP-induced Fermi arcs remains challenging from the material point of view. A pair of TPs are protected by the C 3v symmetry group (generated by a C 3 rotation and a σ v mirror operation) in certain compounds [19-24], for example, tensile-strained HgTe [19], MoP [20], and antiferromagnetic (AFM) half-Heusler compounds (e.g. GdPtBi) [24]. Even presuming that samples can be grown, the natural cleavable surface is usually the facet that is perpendicular to the C 3 axis. Consequently, two TPs at the unique C 3 axis are projected to the same ¯ Γ point of the surface Brillouin zone (BZ), resulting in the disappearance of Fermi arcs, as shown in a recent ARPES measurement on MoP [26]. Therefore, TP materials with easily measurable Fermi arcs are still required for the final experimental verification of TP fermions. In this work, we predict the existence of multiple TPs in several half-Heusler compounds in which the detection of Fermi arcs by ARPE...

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“…From the results of the classical molecular dynamics (MD) simulation of the electrical dipole moment at the interface, it has been suggested that the negative electrical dipole is formed by the migration of metal cations from the high-k dielectrics to SiO 2 . 10,11) These results indicate that the characterization of the chemical structure and bonding features of the high-k=SiO 2 stack is indispensable for obtaining a clear insight into the formation of electrical dipole moments.…”

Section: Introductionmentioning

confidence: 99%

Direct evaluation of electrical dipole moment and oxygen density ratio at high-kdielectrics/SiO₂interface by X-ray photoelectron spectroscopy analysis

Fujimura

Ohta

Ikeda

et al. 2018

Jpn. J. Appl. Phys.

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The electrical dipole moment at an ultrathin high-k (HfO 2 , Al 2 O 3 , TiO 2 , Y 2 O 3 , and SrO)/SiO 2 interface and its correlation with the oxygen density ratio at the interface have been directly evaluated by X-ray photoelectron spectroscopy (XPS) under monochromatized Al Kα radiation. The electrical dipole moment at the high-k/SiO 2 interface has been measured from the change in the cut-off energy of secondary photoelectrons. Moreover, the oxygen density ratio at the interface between high-k and SiO 2 has been estimated from cation core-line signals, such as Hf 4f, Al 2p, Y 3d, Ti 2p, Sr 3d, and Si 2p. We have experimentally clarified the relationship between the measured electrical dipole moment and the oxygen density ratio at the high-k/SiO 2 interface.

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Molecular dynamics study on the formation of dipole layer at high-k/SiO₂interfaces

Cited by 11 publications

References 26 publications

Driving force of oxygen-ion migration across high-k/SiO₂ interface

Driving force of oxygen-ion migration across high-k/SiO₂ interface

Half-Heusler topological insulators

Direct evaluation of electrical dipole moment and oxygen density ratio at high-kdielectrics/SiO₂interface by X-ray photoelectron spectroscopy analysis

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Molecular dynamics study on the formation of dipole layer at high-k/SiO2interfaces

Cited by 11 publications

References 26 publications

Driving force of oxygen-ion migration across high-k/SiO2 interface

Driving force of oxygen-ion migration across high-k/SiO2 interface

Half-Heusler topological insulators

Direct evaluation of electrical dipole moment and oxygen density ratio at high-kdielectrics/SiO2interface by X-ray photoelectron spectroscopy analysis

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Product

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Molecular dynamics study on the formation of dipole layer at high-k/SiO₂interfaces

Driving force of oxygen-ion migration across high-k/SiO₂ interface

Driving force of oxygen-ion migration across high-k/SiO₂ interface

Direct evaluation of electrical dipole moment and oxygen density ratio at high-kdielectrics/SiO₂interface by X-ray photoelectron spectroscopy analysis