Further characterization of oxygen vacancies and zinc vacancies in electron-irradiated ZnO

Evans, S. M.; Giles, N. C.; Halliburton, L. E.; Kappers, L. A.

doi:10.1063/1.2833432

Cited by 134 publications

(115 citation statements)

References 41 publications

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“…41,42,48 On the other hand, under illumination at low temperatures, ionized V Zn can be transformed to the neutral charge state. 49 Detailed investigation of V Zn properties under illumination has been studied by Evans et al 50 In this work, illumination on the ZnO crystal with 325 nm laser light at low temperature produced the electron paramagnetic resonance signal from neutral V 0 Zn and neutral centers (V À Zn , H þ ) 0 , which were not observed before illumination. The localization energy of BE calculated from the energy difference between the FX emission and the 3.33 eV transition is about 40 meV.…”

Section: Implications Of the Experimental Resultsmentioning

confidence: 99%

Study of the photoluminescence emission line at 3.33 eV in ZnO films

Yalishev

Kim

Deng

et al. 2012

Journal of Applied Physics

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We study properties of the line at 3.33 eV observed in photoluminescence (PL) emission spectra of various ZnO films prepared using pulsed laser deposition method. The influence of deposition parameters, such as oxygen pressure, laser fluence, post-annealing, and electric field exposure on intensity of this luminescence band has been investigated. The recombination characteristics are probed by temperature and excitation dependent PL spectroscopy. The obtained experimental data suggest that the 3.33 eV luminescence line in ZnO depends strongly on surface band bending and originates from recombination of bound excitons (BEs) complex located near the surface and grain boundaries. The anomalously small thermal activation energy of BE in comparison with the localization energy is explained by decreasing of the interface barrier. Possible nature of defects that bind free excitons and cause the 3.33 eV emission line in ZnO is proposed. V C 2012 American Institute of Physics. [http://dx

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Section: Implications Of the Experimental Resultsmentioning

confidence: 99%

Study of the photoluminescence emission line at 3.33 eV in ZnO films

Yalishev

Kim

Deng

et al. 2012

Journal of Applied Physics

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“…6͒ without any hyperfine feature was observed with g value of 2.0034 and a line width of 3.5 G for as synthesized unirradiated ZnO:Li powder sample at room temperature. For detection of Li acceptor center, it has been reported that light illumination is necessary 20,21 and such spectra exhibited pronounced hyperfine structure for axial trapped hole ͑g ʈ = 2.0028, g Ќ = 2.0253͒ and for nonaxial Li-O bond direction ͑g xx = 2.0223, g yy = 2.0254, g zz = 2.0040͒. Such centers have been reported to be deep acceptors producing yellow luminescence band ͑2.05 eV͒.…”

Section: Resultsmentioning

confidence: 99%

Room-temperature ferromagnetism in Li-dopedp-type luminescent ZnO nanorods

2009

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We have observed ferromagnetism in Li-doped ZnO nanorods with Curie temperature up to 554 K. Li forms shallow acceptor states in substitutional zinc sites giving rise to p-type conductivity. An explicit correlation emerges between increase in hole concentration with decrease in magnetization and Curie temperature in ZnO:Li. Occurrence of ferromagnetism at room temperature has been established with observed magnetic domain formation in ZnO:Li pellets in magnetic force microscopy and prominent ferromagnetic resonance signal in electron paramagnetic resonance spectrum. Magnetic ZnO:Li nanorods are luminescent, showing strong near UV emission. Substitutional Li atoms can induce local moments on neighboring oxygen atoms, which when considered in a correlated model for oxygen orbitals with random potentials introduced by dopant atom could explain the observed ferromagnetism and high Curie temperature in ZnO:Li nanorods.

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“…This is supported by experiment. By monitoring the optical threshold for ionization of the neutral V O centre, detected using electron paramagnetic resonance (EPR), Evans et al [47] estimated the [0/2+] donor level to lie ∼ 2.1 eV below the CBM. Furthermore, using optical-detected EPR measurements, Vlasenko and Watkins [48] found the [+/0] transition level to lie either 0.9 eV or 2.48 eV above the top of the valence band maximum (VBM).…”

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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Further characterization of oxygen vacancies and zinc vacancies in electron-irradiated ZnO

Cited by 134 publications

References 41 publications

Study of the photoluminescence emission line at 3.33 eV in ZnO films

Study of the photoluminescence emission line at 3.33 eV in ZnO films

Room-temperature ferromagnetism in Li-dopedp-type luminescent ZnO nanorods

Conductivity in transparent oxide semiconductors

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