Identification of Hydrogen Molecules in ZnO

Lavrov, E. V.; Herklotz, F.; Weber, J.

doi:10.1103/physrevlett.102.185502

Cited by 95 publications

(88 citation statements)

References 38 publications

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“…2). This is consistent with the experimental observation of + H i but not H 2 after hydrogenation at high temperature (>1000 °C), 14 which provides a condition close to the thermal equilibrium for H in ZnO. The results shown in Fig.…”

supporting

confidence: 81%

“…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%

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Anionic and Hidden Hydrogen in ZnO

Biswas

2011

Phys. Rev. Lett.

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confidence: 81%

mentioning

confidence: 99%

Anionic and Hidden Hydrogen in ZnO

Biswas

2011

Phys. Rev. Lett.

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“…27 Our experimental data that reveal an electrically inactive source of H, however, suggest that H 2 remains an attractive candidate for a source of hidden hydrogen in our experiments that does not give rise to free-carrier absorption or O-H vibrational lines, similar to the role played by H 2 in ZnO. 32,33 Once a sample has been heat treated at elevated temperature in a H 2 Annealing at elevated temperature (500 ºC here) releases H i from these defects that becomes trapped as the isolated interstitial donor species when the sample is quickly quenched to room temperature.…”

Section: Sources and Sinks For Hydrogenmentioning

confidence: 91%

“…31 When H i decays upon annealing, H 2 molecules are formed that provide a reservoir of hydrogen in the ZnO sample that can be partially converted back to H i by thermal treatments. [31][32][33] H O is a more thermally stable defect than H i and decays upon annealing at ≈500 °C. The H O donor is believed to be the cause of H-related conductivity in as-grown ZnO materials.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen impurities and shallow donors in SnO2studied by infrared spectroscopy

et al. 2011

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Hydrogen has been found to be an important source of n-type conductivity in the transparent conducting oxide SnO 2 . We have studied the properties of H in SnO 2 single crystals with infrared spectroscopy.When H or D is introduced into SnO 2 by annealing in an H 2 or D 2 ambient at elevated temperature, several O-H and O-D vibrational lines are produced along with the low-frequency absorption that is characteristic of free carriers. To probe the relationship between H and the free carriers it introduces, the thermal stability of the free carrier absorption and its relationship to the thermal stabilities of the O-H lines have been examined. Two H-related donors are found, one that is stable at room temperature on a time scale of weeks and a second that is stable up to 600ºC. These electrically active defects are found to interact with other O-H centers and can be converted from one to another by thermal treatments. The vibrational modes have been found to have distinctive polarization properties that provide an important test of microscopic defect models for the several O-H and (O-H) 2 centers that we have observed.2

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“…By analogy, a shallow donor state of hydrogen would also be expected, which was soon-after confirmed by EPR measurements [88]. These works stimulated a flurry of studies on the presence and local bonding environment of interstitial hydrogen in ZnO [46,[89][90][91][92][93][94][95][96][97][98]. In addition, hydrogen has been shown as a viable intentional n-type dopant [99] and co-dopant with Al [100] and Ga [101] in ZnO grown by a variety of techniques ranging from sputtering methods [99] to chemical solution deposition [100].…”

Section: Donor Nature Of Hydrogenmentioning

confidence: 99%

Conductivity in transparent oxide semiconductors

King

Veal

2011

J. Phys.: Condens. Matter

220

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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Identification of Hydrogen Molecules in ZnO

Cited by 95 publications

References 38 publications

Anionic and Hidden Hydrogen in ZnO

Anionic and Hidden Hydrogen in ZnO

Hydrogen impurities and shallow donors in SnO2studied by infrared spectroscopy

Conductivity in transparent oxide semiconductors

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