Investigating Alternative Gate Dielectrics: A Theoretical Approach

Demkov, Alexander A.

doi:10.1002/1521-3951(200107)226:1<57::aid-pssb57>3.0.co;2-l

Cited by 117 publications

(53 citation statements)

References 28 publications

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“…separated by an energy gap of 3.8 eV from a conduction band composed of Hf 5d character. This is in agreement with previous theoretical studies [33][34][35] as well as with the photoemission and inverse photoemission data obtained from HfO 2 deposited on SiO x N y / pSi, which showed that the valence band mainly consists of O 2p nonbonding orbitals of symmetry while the conduction band is primarily Hf 5d-like nonbonding orbitals. 35 However, our calculations show that the upper valence band exhibits mixing of the O 2p and Hf 5d states, indicating covalency of the Hf-O bonds.…”

Section: Electronic Structuresupporting

confidence: 93%

First-principles calculations of structural and electronic properties of monoclinic hafnia surfaces

2006

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We have carried out a systematic theoretical study of the surfaces of monoclinic hafnia ͑HfO 2 ͒ using plane waves and density functional theory based on the generalized gradient approximation. The fully relaxed structures of the bulk phases of HfO 2 are found to be in excellent agreement with experimental data, the monoclinic phase being the most stable. Simulations of the monoclinic phase surfaces indicate a large relaxation which reduces the total surface energy of all nine faces considered by between 23% and 36%, with a strong correlation between the unrelaxed and relaxed surface energies. Our calculations predict that the ͑111͒ and ͑111͒ faces of the monoclinic phase have the lowest surface energies and are hence the most stable faces. An analysis of the total and partial electronic density of states of bulk monoclinic HfO 2 reveals that the outer valence band significantly mixes the O 2p and Hf 5d atomic states indicating some covalency of the Hf-O bonds. The total density and partial density of states of the monoclinic surfaces exhibit a surface state corresponding to the surface O 2s states in the inner valence band region.

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Section: Electronic Structuresupporting

confidence: 93%

First-principles calculations of structural and electronic properties of monoclinic hafnia surfaces

2006

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“…Our results are also in good agreement with previous DFT calculations of this material. 35 Note however, that the experimental data for cubic and tetragonal phases are taken at high temperature, e.g., 2073 K for tetragonal, and are also somewhat dependent on temperature, and therefore comparisons with the 0 K theoretical data are limited. The electron density of states ͑DOS͒ for ideal monoclinic hafnia is shown in Fig.…”

Section: A Ideal Crystalsmentioning

confidence: 99%

Vacancy and interstitial defects in hafnia

et al. 2002

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We have performed plane wave density functional theory calculations of atomic and molecular interstitial defects and oxygen vacancies in monoclinic hafnia (HfO 2 ). The atomic structures of singly and doubly positively charged oxygen vacancies, and singly and doubly negatively charged interstitial oxygen atoms and molecules are investigated. We also consider hafnium vacancies, substitutional zirconium, and an oxygen vacancy paired with substitutional zirconium in hafnia. Our results predict that atomic oxygen incorporation is energetically favored over molecular incorporation, and that charged defect species are more stable than neutral species when electrons are available from the hafnia conduction band. The calculated positions of defect levels with respect to the bottom of the silicon conduction band demonstrate that interstitial oxygen atoms and molecules and positively charged oxygen vacancies can trap electrons from silicon.

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“…Vibrational spectroscopy studies and theoretical work on zirconia have been performed, 1,[12][13][14][15] and other studies were focused on phase transitions under pressure.…”

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confidence: 99%

Phonon anharmonicity of monoclinic zirconia and yttrium-stabilized zirconia

Smith

Lan

et al. 2015

Phys. Rev. B

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Inelastic neutron scattering measurements on monoclinic zirconia (ZrO2) and 8 mol% yttriumstabilized zirconia were performed at temperatures from 300 to 1373 K. Temperature-dependent phonon densities of states (DOS) are reported, as are Raman spectra obtained at elevated temperatures. First-principles lattice dynamics calculations with density functional theory gave total and partial phonon DOS curves, and mode Grüneisen parameters. These mode Grüneisen parameters were used to predict the experimental temperature dependence of the phonon DOS, with partial success. However, substantial anharmonicity was found at elevated temperatures, especially for phonon modes dominated by the motions of oxygen atoms. Yttrium-stabilized zirconia (YSZ) was somewhat more anharmonic, and had a broader phonon spectrum at low temperatures, owing in part to defects in its structure. YSZ also has a larger vibrational entropy than monoclinic zirconia.

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Investigating Alternative Gate Dielectrics: A Theoretical Approach

Cited by 117 publications

References 28 publications

First-principles calculations of structural and electronic properties of monoclinic hafnia surfaces

First-principles calculations of structural and electronic properties of monoclinic hafnia surfaces

Vacancy and interstitial defects in hafnia

Phonon anharmonicity of monoclinic zirconia and yttrium-stabilized zirconia

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