Density functional theory model of amorphous zinc oxide (a-ZnO) and a-X0.375Z0.625O (X= Al, Ga and In)

Pandey, Anup; Scherich, Heath; Drabold, D. A.

doi:10.1016/j.jnoncrysol.2016.10.035

Cited by 10 publications

(7 citation statements)

References 23 publications

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“…On the other hand, some degree of localization of VBM states suggests that disorder can lead to hole localization upon structural relaxation. Similar asymmetry in the character of localization VBM and CBM states has also been seen in other amorphous oxides, such as In 2 O 3 , IGZO, Al 2 O 3 …”

Section: Resultssupporting

confidence: 77%

“…Similar asymmetry in the character of localization VBM and CBM states has also been seen in other amorphous oxides, such as In 2 O 3 , IGZO, Al 2 O 3 . [21,38,105,106,[108][109][110] The average a-ZnO band gap is ≈3.36 eV, 0.15 eV lower than that in the crystalline phase, with a standard deviation of 0.08 eV. The latter is in line with experiments, [111] where oxides with large cations (r i ≳ 0.7 Å) show no significant band gap difference between the crystalline and amorphous phase, whereas gap widening is observed for more compact cations.…”

Section: Electronic Structure Of A-znosupporting

confidence: 85%

“…Amid largely unsuccessful attempts to grow good quality a‐ZnO films, theoretical predictions of a‐ZnO have been more optimistic. Stable a‐ZnO structures have been produced using mainly ab initio molecular dynamics (MD) melt and quench (MQ) methods . These computationally demanding calculations use small periodic cells, very high cooling rates, and provide limited statistics of structural characteristics.…”

Section: Introductionmentioning

confidence: 99%

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Modeling of Intrinsic Electron and Hole Trapping in Crystalline and Amorphous ZnO

Mora‐Fonz

Shluger

2019

Adv Elect Materials

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Furthermore, even thermodynamically stable phases, for example, zincblende or rocksalt, are only grown under very specific conditions of substrates and/or at high pressure (see, e.g., refs. [8-12]). Although successful growth of thin a-ZnO films with thicknesses ranging from 5 to 100 nm using different techniques and on different substrates has been reported, [13-18] the morphology of these films remains controversial due to the lack of high intensity X-ray diffraction or grazing incidence X-ray and neutron diffraction characterization. Many of such films are reported to contain nanocrystalline inclusions. [13,16,18-20] Amid largely unsuccessful attempts to grow good quality a-ZnO films, theoretical predictions of a-ZnO have been more optimistic. Stable a-ZnO structures have been produced using mainly ab initio molecular dynamics (MD) melt and quench (MQ) methods. [21-26] These computationally demanding calculations use small periodic cells, very high cooling rates, and provide limited statistics of structural characteristics. The sampling of the a-ZnO configurational space has been, therefore, poor and a distribution of electronic properties has not been provided yet. Recently, we investigated the ability of bulk ZnO to form glass structures using interatomic potentials (IPs) and an MQ procedure within isothermal-isobaric (NPT) ensemble. [27] This allowed us to use large (up to 768 000 atoms) periodic cells and improve the statistics of the distribution of a-ZnO structural characteristics. These calculations have demonstrated that cooling rates in an MQ procedure around 100 K ps −1 lead to the formation of stable and uniform amorphous structures. ZnO samples show, however, different degrees of crystallinity at lower cooling rates. The average density of a-ZnO samples produced using IPs is about 5.04 g cm −3 and the coordination numbers of Zn and O atoms are around 3.9, reflecting the strong propensity to crystallization. Still, the stability tests carried out using the activation-relaxation technique (ART) [28-32] and simulated annealing demonstrated that the obtained amorphous structures are stable. [27] Advances in ultrafast liquid quenching and deposition of thin films on cold substrates [33-36] make achieving growth of amorphous ZnO films a tangible prospect. Their potential use in (photo)electronic devices will expose these films to electrons and holes. Therefore, questions arise whether a-ZnO films will retain good electron mobility and whether there is any possibility for electron or hole localization due to disorder. Such Recent advances in ultrafast liquid quenching and deposition of thin films on cold substrates make growing amorphous (a)-ZnO films increasingly feasible. The electronic structure and electron and hole trapping properties of amorphous ZnO are predicted using density functional theory (DFT) simulations with a hybrid density functional (h-DFT). An ensemble of fifty 324-atom structures is employed to obtain the distribution of structural and electronic properties of a-ZnO. The results demon...

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Section: Resultssupporting

confidence: 77%

Section: Electronic Structure Of A-znosupporting

confidence: 85%

Section: Introductionmentioning

confidence: 99%

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Modeling of Intrinsic Electron and Hole Trapping in Crystalline and Amorphous ZnO

Mora‐Fonz

Shluger

2019

Adv Elect Materials

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“…It can be compared to the random networks of III-V compounds like a-GaAs. Unlike a-GaAs, a-ZnO is a fully chemically ordered network with no likeatom bond, Fig 1(b) [53]. As in a-GaAs, the other possible defect in a-ZnO is the mis-coordinated atom for example 3-fold Zn or 3-fold O.…”

Section: Bulk Znomentioning

confidence: 99%

Oxygen vacancies and hydrogen in amorphous In-Ga-Zn-O and ZnO

Guo

Robertson

2018

Phys. Rev. Materials

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Hydrogen is known to be present as an impurity in amorphous oxide semiconductors at the 0.1% level. The behavior of hydrogen and oxygen vacancies in amorphous In-Ga-Zn-O is studied using density functional supercell calculations. We show that the hydrogens pair up at oxygen vacancies in the amorphous network, where they form metal-H-metal bridge bonds. These bonds are shown to create filled defect gap states lying just above the valence band edge, infra-red modes at about 1400 and 1520 cm-1 , and they are shown to give a consistent mechanism to explain the negative bias illumination stress instability found in oxide semiconductors like In-Ga-Zn-O (IGZO).

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“…The computer power and the accuracy of theoretical approaches have recently increased significantly, allowing the use of computational tools to understand the behaviour of metal oxides such as ZnO. The utility of computational methods to understand the electronic and optical properties of ZnO has been reviewed [15,16] and their use is becoming more and more popular [17,18,19,20,21,22,23]. It is well known that Car-Parrinello molecular dynamics (CPMD) [24], combined with metadynamics algorithms [25], are powerful tools for studying a large variety of systems, from condensed-matter physics to chemical processes, and can provide a reasonable estimation of the successive paths of a chemical transformation [26,27,28,29,30,31,32,33].…”

Section: Introductionmentioning

confidence: 99%

From Ethanolamine Precursor Towards ZnO—How N Is Released from the Experimental and Theoretical Points of View

et al. 2019

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This work presents experimental and computational studies on ZnO formation after decomposition of a sol-gel precursor containing ethanolamine and Zn(II) acetate. The structural modifications suffered during decomposition of the monomeric and dimeric Zn(II) complexes formed, containing bidentate deprotonated ethanolamine and acetato ligands, have been described experimentally and explained via Car-Parrinello Molecular Dynamics. Additional metadynamics simulations provide an overview of the dimer evolution by the cleavage of the Zn–N bond, the structural changes produced and their effects on the Zn(II) environment. The results provide conclusive evidence of the relevance of ethanolamine used as a stabilizer in the formation of ZnO.

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Density functional theory model of amorphous zinc oxide (a-ZnO) and a-X0.375Z0.625O (X= Al, Ga and In)

Cited by 10 publications

References 23 publications

Modeling of Intrinsic Electron and Hole Trapping in Crystalline and Amorphous ZnO

Modeling of Intrinsic Electron and Hole Trapping in Crystalline and Amorphous ZnO

Oxygen vacancies and hydrogen in amorphous In-Ga-Zn-O and ZnO

From Ethanolamine Precursor Towards ZnO—How N Is Released from the Experimental and Theoretical Points of View

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