Oxygen vacancies in ZnO

Janotti, Anderson; Walle, Chris G. Van de

doi:10.1063/1.2053360

Cited by 1,080 publications

(843 citation statements)

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“…Using thermodynamic arguments, Kohan and co-workers, 51 Zhang and co-workers, 36 Janotti and van de Walle, 55 and the present author ͑this work͒ have found that the V O defect is a negative-U defect. The value of U is the difference, ⑀͑+͉0͒ − ⑀͑2+͉ + ͒, since this equals the difference in formation energies…”

Section: Fig 11 Spin Density For Two Co Ions and A V Omentioning

confidence: 56%

“…55͒, and −0.6 eV ͑this work͒. The ⑀͑2+͉0͒ transition level is found at −0.6 eV, 36 −1.0 eV, 55 or at −3.0 eV ͑this work͒. The calculation described above, in which two V O and one V Zn vacancies were placed in the same 3 ϫ 3 ϫ 2 supercell, as well as the relative ordering of ⑀͑+͉0͒, ⑀͑2+͉ + ͒, and ⑀͑2+͉0͒, confirm that V O is a negative-U defect, so it is unlikely that isolated V O defects are the main mediators of ferromagnetism in Zn 1−x Co x O.…”

Section: Fig 11 Spin Density For Two Co Ions and A V Omentioning

confidence: 87%

“…Thermodynamic arguments, 36 to be 1.0, 55 2.4, 36 or 3.3 eV ͑this work͒ below the CBM; a nonlinear spectroscopy study 61 found this level to lie 2.1 eV below the CBM.…”

Section: A Single Defectsmentioning

confidence: 97%

“…36 and 55͒ or B3LYP calculations ͑this work͒, and therefore support a model in which the V O defect is the lower level in the transition. However, the ⑀͑0 ͉ + ͒ level is shifted up in the band gap in an LDA+ U calculation 55 …”

Section: A Single Defectsmentioning

confidence: 99%

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Role of defects in ferromagnetism inZn1−xCoxO: A hybrid density-functional study

2006

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Section: Fig 11 Spin Density For Two Co Ions and A V Omentioning

confidence: 56%

Section: Fig 11 Spin Density For Two Co Ions and A V Omentioning

confidence: 87%

“…Thermodynamic arguments, 36 to be 1.0, 55 2.4, 36 or 3.3 eV ͑this work͒ below the CBM; a nonlinear spectroscopy study 61 found this level to lie 2.1 eV below the CBM.…”

Section: A Single Defectsmentioning

confidence: 97%

Section: A Single Defectsmentioning

confidence: 99%

See 2 more Smart Citations

Role of defects in ferromagnetism inZn1−xCoxO: A hybrid density-functional study

2006

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“…The variations in magnitude of the formation energy for the oxygen vacancy between different calculations leads to orders-of-magnitude differences in the concentration of these defects expected from thermodynamic considerations. For example, a high formation energy of the oxygen vacancy for Fermi levels close to the CBM, as calculated by Janotti and Van de Walle [49,51] and Lee et al [52], would suggest negligible concentrations of such defects under equilibrium conditions. In contrast, from the much lower formation energies calculated by Lany and Zunger [53] and Erhart et al [54], much higher defect concentrations would be expected, up to ∼ 10 20 cm −3 under favourable conditions.…”

Section: Oxygen Vacanciesmentioning

confidence: 99%

Conductivity in transparent oxide semiconductors

King

Veal

2011

J. Phys.: Condens. Matter

224

180

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Abstract. Despite an extensive research effort for over 60 years, an understanding of the origins of conductivity in wide band-gap transparent conducting oxide (TCO) semiconductors remains elusive. While TCOs have already found widespread use in device applications requiring a transparent contact, there are currently enormous efforts to (i) increase the conductivity of existing materials, (ii) identify suitable alternatives, and (iii) attempt to gain semiconductor-engineering levels of control over their carrier density, essential for the incorporation of TCOs into a new generation of multifunctional transparent electronic devices. These efforts, however, are dependent on a microscopic identification of the defects and impurities leading to the high unintentional carrier densities present in these materials. Here, we review recent developments towards such an understanding. While oxygen vacancies are commonly assumed to be the source of the conductivity, there is increasing evidence that this is not a sufficient mechanism to explain the total measured carrier concentrations. In fact, many studies suggest that oxygen vacancies are deep, rather than shallow, donors, and their abundance in as-grown material is also debated. We discuss other potential contributions to the conductivity in TCOs, including other native defects, their complexes, and in particular hydrogen impurities. Convincing theoretical and experimental evidence is presented for the donor nature of hydrogen across a range of TCO materials, and while its stability and the presence of interstitial and substitutional species are still somewhat open questions, it is one of the leading contenders for unintentional conductivity in TCOs. We also review recent work indicating that the surfaces of TCOs can support very high carrier densities, opposite to the case of conventional semiconductors. In thin-film materials/devices and, in particular, nanostructures, the surface can have a large impact on the total conductivity in TCOs. We discuss models that attempt to explain both the bulk and surface conductivity based on features of the bulk band structure common across the TCOs, and compare these materials to other semiconductors. Finally, we briefly consider transparency in these materials, and its interplay with conductivity. Understanding this interplay, as well as the microscopic contenders for the conductivity of these materials, will prove essential to the future design and control of TCO semiconductors, and their implementation into novel multifunctional devices.

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