In this study, we investigate the role of oxygen vacancies for the orthorhombic noncentrosymmetric Pbc21 Hf0.5Zr0.5O2 stabilization by means of ab initio calculations. The comparative analysis of the ...calculated data for stable and different orthorhombic Hf0.5Zr0.5O2 phases revealed that an oxygen vacancy leads to the ferroelectric Pbc21-Hf0.5Zr0.5O2 phase destruction in case of oxygen-vacancy-rich conditions.
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•The VO concentration increasing narrows pressure range of the o-Hf0.5Zr0.5O2 stability.•High VO concentration has a positive impact on the Pnma-Hf0.5Zr0.5O2 stabilization.•The of-Hf0.5Zr0.5O2 with a high VO concentration is not stable in a bulk crystal.•The VO generation leads to ferroelectricity destruction in the O-poor conditions.
The oxygen vacancy, interstitial oxygen and hafnium, hafnium substituting oxygen and oxygen Frenkel pair in HfO2 are the probable defects which are able to participate in the conducting filament ...formation in hafnia-based RRAM. In this paper, we studied the atomic and electronic structures of above-listed defects within the first principles simulation. It was found that all studied defects can be involved in the charge transport. Oxygen vacancies are the key defects for the charge transport and RRAM operability. It was suggested that interstitial oxygen atoms make a significant contribution to the HfO2 hole conductivity. The hafnium interstitial competes with an oxygen interstitial and the Frenkel pair in the conducting filament formation in O-poor conditions. The oxygen vacancies and hafnium substituting oxygen pairs atomic structure indicate a tendency to these defects clustering.
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•Vacancies are a key defects in HfO2 transport and conducting filament formation.•Interstitial makes a significant contribution to the HfO2 hole conductivity.•Hf interstitial compete with O interstitial in a filament forming in the O-poor case.•Atomic structure of O vacancies and Hf substituting O pairs exhibit their clustering.
Cubic, tetragonal, and monoclinic phases of zirconium oxide with oxygen vacancies and polyvacancies are studied by quantum chemical modeling of the atomic and electronic structure. It is demonstrated ...that an oxygen vacancy in ZrO
2
may act as both an electron trap and a hole one. An electron added to the ZrO
2
structure with an oxygen vacancy is distributed between two neighboring Zr atoms and is a bonding orbital by nature. It is advantageous for each subsequent O vacancy to form close to the already existing ones; notably, one Zr atom has no more than two removed O atoms related to it. Defect levels from oxygen polyvacancies are distributed in the bandgap with preferential localization in the vicinity of the oxygen monovacancy level.
One of the most important issues during the selection of low-
k
dielectrics is related to their intrinsic properties including their electric breakdown and leakage current that are predominantly ...determined by conduction mechanisms. This study is devoted to elucidating the charge transport mechanism in the SiOCH low-
k
dielectric films fabricated by plasma-enhanced chemical vapor deposition. By analyzing four bulk-limited models of the charge transport it was found that only the Nasyrov–Gritsenko model of phonon-assisted electron tunneling between neutral traps describes the experimental
I
–
V
–
T
characteristics with all the fitting parameters with reasonable physical values. The obtained thermal trap energy value 1.2 eV is confirmed independently by photoluminescence spectroscopy data analysis. The trap nature and comparison of the obtained results with the corresponding data for low-
k
films with similar chemical composition and deposited by the spin-on-glass technology using self-assembling chemistry is discussed. It is hypothesized that the defect with ionization energy of 1.2 eV is the oxygen divacancy.
A mechanism of transverse charge transfer through hexagonal boron nitride (h-BN) in a MIS structure has been studied. Experimental data for charge transfer have been analyzed in terms of different ...models of charge transfer in insulators. It has been shown that charge transfer in h-BN is described by the model of phonon-assisted tunneling between neutral traps. The thermal and optical energies of phonon-coupled traps in h-BN have been determined. Based on charge transfer measurements, XPS spectra, and the ab initio electronic structure of intrinsic defects in h-BN it has been found that boron–nitrogen divacancies are most probably responsible for charge transfer in h-BN and transfer is provided by electrons.
It is shown that the treatment of stoichiometric HfO
2
, which is synthesized by atomic layer deposition, in electron cyclotron resonance hydrogen plasma leads to a significant depletion of the film ...in oxygen and the formation of nonstoichiometric HfO
x
(
). The longer the treatment time, the higher the degree of oxygen depletion. The charge transfer in the films under study occurs by phonon-assisted tunneling between oxygen vacancies serving as traps. It has been found that the
-Si/HfO
x
/Ni structures, where the oxide layer is treated in the electron cyclotron resonance hydrogen plasma, have memristor properties: they are reversibly switched between high and low resistance states. The fabricated memristor structures are forming-free.
Titanium dioxide (anatase, a-TiO
2
) films have been prepared by electron beam sputtering of a TiO
2
target in reactive atmosphere and their structural, microstructural, and optical properties were ...evaluated by reflection high- energy electron diffraction (RHEED) and x-ray diffraction (XRD) analyses, atomic force microscopy (AFM), and spectroscopic ellipsometry (SE). Different reflection models for determination of film optical parameters were tested and compared. The dispersive optical parameters were defined using the Tauc–Lorentz model by SE in the photon energy range of
E
= 1.12–4.96 eV. The films were transparent at
E
< 3 eV, but noticeable absorption was detected at
E
> 3 eV. The bandgap was estimated at the level of
E
g
≈ 3.44 eV.
The atomic and electronic structure of intrinsic point defects in orthorhombic tantalum oxide has been studied by numerical simulation within the density functional theory. It has been shown that all ...defects responsible for metal enrichment of Ta
2
O
5
serve as electron and hole traps. Under conditions of strong oxygen depletion and at a metal–insulator interface, which are characteristic of resistive memory elements, interstitial tantalum atoms compete with an oxygen vacancy in the formation of a conducting filament. Interstitial oxygen atoms are not involved in charge transport. Tantalum substituting oxygen can be considered as a combination of the oxygen vacancy and interstitial tantalum. The analysis of the calculated thermal and optical energies of trap ionization shows that the oxygen vacancy is a key defect for charge transport in Ta
2
O
5
.
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•We calculate XPS and absorption spectra for crystalline HfO2 in frame of hybrid DFT.•We got the experimental XPS for bombarding with Ar-ions hafnia and HfOx.•Oxygen vacancies in HfO2 ...produce the defect states at 3.0eV above the valence band.•Ar+ ion bombardment of HfO2 produces the oxygen vacancies and polyvacancies.•Absorption peak at 3.0–4.5eV for HfO2 is attributed to the oxygen vacancy.
The electronic structure of oxygen vacancies and polyvacancies in HfO2 was studied theoretically from the first-principles calculations and experimentally, by X-ray photoelectron spectroscopy. The electronic structure calculations of crystalline HfO2 were performed within the hybrid density functional theory. The experimental photoelectron spectra indicate that both nonstoichiometric chemistry and Ar-ion bombardment of hafnia films lead to the generation of the defect states at 3.0eV above the valence band. According to the calculations, these defect states are attributed to the oxygen vacancies.
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