Electronic Structure of the Muonium Center as a Shallow Donor in ZnO

Shimomura, K.; Nishiyama, K.; Kadono, R.

doi:10.1103/physrevlett.89.255505

Cited by 107 publications

(76 citation statements)

References 17 publications

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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: 80%

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: Donor Nature Of Hydrogenmentioning

confidence: 80%

Conductivity in transparent oxide semiconductors

King

Veal

2011

J. Phys.: Condens. Matter

224

180

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“…When easily resolved, the amplitudes of the central line and satellites provide a measure of Mu + and Mu 0 fractions and it is their variation with temperature in an equilibrium model that has hitherto been analysed for ionization energy or donor depth (Gil et al 2001a, Cox et al 2001a, Shimomura et al 2002. In fact, it is not obvious whether a dynamic or thermal equilibrium between Mu 0 and Mu + can be assumed if the satellites remain visible.…”

Section: The Shallow-donor Muonium State In Zno-a Reappraisalmentioning

confidence: 99%

“…Table 2 gives a compendium of all paramagnetic muonium states found so far in non-magnetic binary oxides, including results from the accompanying Paper I and older µSR literature. Shallow-donor states are observed or are inferred with reasonable confidence in BaO, CeO 2 , CdO, HfO 2 (monoclinic), Li 2 O, SnO 2 , SrO, TiO 2 (both anatase and rutile), WO 3 , Y 2 O 3 , ZnO Shimomura et al (2002). Band-gap and oxygen coordination for the host materials are tabulated (from literature compilations) to aid the search for systematics: see also Hjelm et al (1996).…”

Section: The Vacancy Complex and Bridging Sitementioning

confidence: 99%

Oxide muonics: II. Modelling the electrical activity of hydrogen in wide-gap and high-permittivity dielectrics

Cox

Gavartin

Lord

et al. 2006

J. Phys.: Condens. Matter

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Following the prediction and confirmation that interstitial hydrogen forms shallow donors in zinc oxide, inducing electronic conductivity, the question arises as to whether it could do so in other oxides, not least in those under consideration as thin-film insulators or high-permittivity gate dielectrics. We have screened a wide selection of binary oxides for this behaviour, therefore, using muonium as an accessible experimental model for hydrogen. New examples of the shallow-donor states that are required for n-type doping are inferred from hyperfine broadening or splitting of the muon spin rotation spectra. Electron effective masses are estimated (for several materials where they are not previously reported) although polaronic rather than hydrogenic models appear in some cases to be appropriate. Deep states are characterized by hyperfine decoupling methods, with new examples found of the neutral interstitial atom even in materials where hydrogen is predicted to have negative-U character, as well as a highly anisotropic deep-donor state assigned to a muonium-vacancy complex. Comprehensive data on the thermal stability of the various neutral states are given, with effective ionization temperatures ranging from 10 K for the shallow to over 1000 K for the deep states, and corresponding activation energies between tens of meV and several eV. A striking feature of the systematics, rationalized in a new model, is the preponderance of shallow states in materials with band-gaps less below 5 eV, atomic states above 7 eV, and their coexistence in the intervening threshold range, 5-7 eV.

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“…In Fig.4a shown are the µTC setup and vertical helium flow cryostat as installed in ARTEMIS. In order to measure the anisotropy of hyper-fine parameter of shallow muonium state, such as in ZnO [5] and rutile TiO 2 [6], an automated sample rotating rod, with the rotation axis parallel to the beam axis is prepared (Fig.4b); with the µTC and vertical helium flow cryostat, the angle dependence measurement of the hyperfine coupling parameter of the shallow muonium state is now fully automated. An example of a Fast Fourier Transform spectrum of the shallow muonium state in ZnO is shown in Fig.4c. (a) …”

Section: Sample Environmentmentioning

confidence: 99%

Development of General Purpose μSR Spectrometer ARTEMIS at S1 Experimental Area, MLF J-PARC

Kojima

Hiraishi

Koda

et al. 2018

Proceedings of the 14th International Conference on Muon Spin Rotation, Relaxation and Resonance (ΜSR2017)

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We have developed a general purpose µSR spectrometer ARTEMIS and installed at S1 experimental area of MLF, J-PARC. The new spectrometer has the identical design with the D1-spectrometer developed in 2013; the common design of the two general purposes spectrometers helps sharing the sample environment apparatus and direct comparison of the beam characteristics between the two experimental areas. We have upgraded the front-end circuit of positron/electron detectors, and achieved high enough hit rate tolerance for muon beam available in the future 1 MW operation of MLF. Other revisions and modifications, which became necessary after the commissioning and the actual usage of the S1/D1 spectrometers have been applied to both of the twin spectrometers.

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Electronic Structure of the Muonium Center as a Shallow Donor in ZnO

Cited by 107 publications

References 17 publications

Conductivity in transparent oxide semiconductors

Conductivity in transparent oxide semiconductors

Oxide muonics: II. Modelling the electrical activity of hydrogen in wide-gap and high-permittivity dielectrics

Development of General Purpose μSR Spectrometer ARTEMIS at S1 Experimental Area, MLF J-PARC

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