First-Principles Study of the Diffusion of Hydrogen in ZnO

Wardle, M. G.; Goss, Jonathan P.; Briddon, P.R.

doi:10.1103/physrevlett.96.205504

Cited by 202 publications

(187 citation statements)

References 36 publications

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“…Wardle et al [112] investigated the diffusion of hydrogen in ZnO from DFT calculations, finding low migration barriers, suggesting that interstitial hydrogen is indeed very mobile in ZnO. However, they suggested that hydrogen could still contribute to conductivity in ZnO, even at elevated temperatures, if it becomes trapped at other existing defect centres.…”

Section: Stabilitymentioning

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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Section: Stabilitymentioning

confidence: 99%

Conductivity in transparent oxide semiconductors

King

Veal

2011

J. Phys.: Condens. Matter

224

180

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“…Forming gas contains H, and isolated H atoms are known to move rather easily in ZnO. [8][9][10][11][12][13][14] In fact, even the most stable member of this class, substitutional H O , is believed to completely diffuse out of the sample for temperatures higher than about 475°C. 12 H can also attain stability by forming complexes with certain impurities and defects, 13 such as the Zn vacancy V Zn , 8,13 Cu, 8 and N. 14 For example, the neutral complex V Zn H 2 is stable to about 400°C.…”

Section: ͑4͒mentioning

confidence: 99%

Mobility analysis of highly conducting thin films: Application to ZnO

Look

Leedy

Tomich

et al. 2010

Applied Physics Letters

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Hall-effect measurements have been performed on a series of highly conductive thin films of Ga-doped ZnO grown by pulsed laser deposition and annealed in a forming-gas atmosphere (5% H2 in Ar). The mobility as a function of thickness d is analyzed by a simple formula involving only ionized-impurity and boundary scattering and having a single fitting parameter, the acceptor/donor concentration ratio K=NA/ND. For samples with d=3–100 nm, Kavg=0.41, giving ND=4.7×1020 and NA=1.9×1020 cm−3. Thicker samples require a two-layer formulation due to inhomogeneous annealing.

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“…11,12 In both cases, the majority of the H donor, i.e., H i + , is eliminated. 28 As a result, the carrier density is substantially lowered.…”

mentioning

confidence: 99%

“…2 Hydrogen in ZnO has been extensively studied in the last ten years 3,4,5,6,7,8,9,10,11,12,13,14,15 because unintentionally doped H is usually found in ZnO, including many commercial ZnO samples. 6 Interstitial and substitutional H have been shown by first-principles calculations to be shallow donors (i.e., + H i and + O H ), which contribute to the n-type conductivity in ZnO.…”

mentioning

confidence: 99%

Anionic and Hidden Hydrogen in ZnO

Biswas

2011

Phys. Rev. Lett.

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First-Principles Study of the Diffusion of Hydrogen in ZnO

Cited by 202 publications

References 36 publications

Conductivity in transparent oxide semiconductors

Conductivity in transparent oxide semiconductors

Mobility analysis of highly conducting thin films: Application to ZnO

Anionic and Hidden Hydrogen in ZnO

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