Intrinsic electron trapping in amorphous oxide

Strand, Jack; Kaviani, Moloud; Afanasʼev, Valeri; Lisoni, J. G.; Shluger, Alexander L.

doi:10.1088/1361-6528/aaa77a

Cited by 36 publications

(51 citation statements)

References 69 publications

(99 reference statements)

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“…The estimated density of such sites [23] in a-HfO 2 is about 2×10 21 cm −3 . The structure and spectroscopic properties of these electron traps are described in detail in Kaviani et al [23] and Strand et al [51]. The bi-polaron formation causes strong Hf-O bond weakening manifested in significant (about 0.8 Å) ionic displacements.…”

Section: Role Of Electron Injection In O-vacancy Creationmentioning

confidence: 98%

Mechanisms of Oxygen Vacancy Aggregation in SiO2 and HfO2

et al. 2019

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Dielectric oxide films in electronic devices undergo significant structural changes during device operation under bias. These changes are usually attributed to aggregation of oxygen vacancies resulting in formation of oxygen depleted regions and conductive filaments. However, neutral oxygen vacancies have high diffusion barriers in ionic oxides and their interaction and propensity for aggregation are still poorly understood. In this paper we briefly review the existing data on static configurations of neutral dimers and trimers of oxygen vacancies in technologically relevant SiO 2 and HfO 2 and then provide new results on the structure and properties of these defects in amorphous SiO 2 and HfO 2. These results demonstrate weak interaction between neutral O vacancies, which does not explain their quick aggregation. We propose that trapping of electrons, injected from an electrode, by the vacancies may result in creation of new neutral vacancies in the vicinity of pre-existing vacancies. We describe this mechanism in a-SiO 2 and demonstrate that this process becomes more efficient as the vacancy clusters grow larger.

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Section: Role Of Electron Injection In O-vacancy Creationmentioning

confidence: 98%

Mechanisms of Oxygen Vacancy Aggregation in SiO2 and HfO2

et al. 2019

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“…The degree of localization of these states was further analyzed by calculating the IPR spectrum, which has been used to characterise the localization of electronic states in amorphous materials including TiO 2 [41,42] and other (more complex) amorphous structures, see, e.g., Refs. [56,69,110,111]. IPR is calculated for each energy eigenstate of the system and the formulation used here has been reported previously [56].…”

Section: B Atomic Structure Of A-tiomentioning

confidence: 99%

Disorder-induced electron and hole trapping in amorphous TiO2

2020

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Thin films of amorphous (a)-TiO 2 are ubiquitous as photocatalysts, protective coatings, photo-anodes, and in memory applications, where they are exposed to excess electrons and holes. We investigate trapping of excess electrons and holes in the bulk of pure amorphous titanium dioxide, a-TiO 2 , using hybrid density-functional theory (h-DFT) calculations. Fifty 270-atom a-TiO 2 structures were produced using classical molecular dynamics and their geometries fully optimized using h-DFT simulations. They have the density, distribution of atomic coordination numbers, and radial pair-distribution functions in agreement with experiments. The calculated average a-TiO 2 band gap is 3.25 eV with no states splitting into the band gap. Trapping of excess electrons and holes in a-TiO 2 is predicted at precursor sites, such as elongated Ti-O bonds. Single electron and hole polarons have average trapping energies (E T) of −0.4 eV and −0.8 eV, respectively. We also identify several types of electron and hole bipolaron states and discuss their stability. These results can be used for understanding the mechanisms of photo-catalysis and improving the performance of electronic devices employing a-TiO 2 films.

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“…In reduced HfO 2 films electrons can be trapped into even deeper states by neutral O vacancies [14], and in amorphous films they can be trapped at low-coordinated Hf sites [43,44]. The localization of two electrons in HfO 2 was shown to significantly reduce the barrier height for DP creation [14,44]. Thus, the bias application causes the electron injection, and the extra electrons reduce barriers for formation of O vacancies.…”

Section: B Effect Of Electron Injectionmentioning

confidence: 99%

Effect of electric field on defect generation and migration in HfO2

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Larcher³

et al. 2020

Phys. Rev. B

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Understanding the effect of electric fields on defect creation and diffusion in metal oxides is of fundamental importance for developing accurate models of oxide degradation in electronic devices and dielectric breakdown. We use the Berry phase operator method within density functional theory to calculate how an applied electric field affects barriers for the creation of oxygen vacancy-interstitial defect pairs (DPs) and diffusion of interstitial O ions in monoclinic (m-)HfO 2. The results demonstrate that even close to breakdown fields, barriers for DP generation exceed 6 eV in the perfect m-HfO 2 lattice. Simulated injection of extra electrons from electrodes significantly lowers barriers for the creation of DPs, which are further reduced by the field to around 1 eV. Thus, bias application facilitates the injection of electrons into the oxide; these extra electrons reduce energy barriers for the creation of O vacancies, and these barriers as well as those for O ion diffusion are further lowered by the field. We find that, within a linear regime, the electric field modulates the barrier height by a dot product between the electric field and the electric dipole at the zero-field transition state to good accuracy.

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Intrinsic electron trapping in amorphous oxide

Cited by 36 publications

References 69 publications

Mechanisms of Oxygen Vacancy Aggregation in SiO2 and HfO2

Mechanisms of Oxygen Vacancy Aggregation in SiO2 and HfO2

Disorder-induced electron and hole trapping in amorphous TiO2

Effect of electric field on defect generation and migration in HfO2

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