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King, P. D. C.; Veal, T. D.; Fuchs, F.; Wang, Ch. Y.; Payne, David J.; Bourlange, A.; Zhang, H.; Bell, Gavin R.; Cimalla, V.; Ambacher, O.; Egdell, R.G.; Bechstedt, F.; McConville, Christopher F

doi:10.1103/physrevb.79.205211

Cited by 383 publications

(233 citation statements)

References 47 publications

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“…Zhang et al [136] employed energy-dependent photoemission, utilizing the inherent variation in surface specificity with photon energy to support this conclusion, providing spectroscopic confirmation of the increased electron density at In 2 O 3 surfaces. Via extrinsic Sn-doping to increase the bulk carrier concentration, it is possible to quench the electron accumulation [134,135]. This provides a mechanism to reconcile these recent results with earlier studies which suggested a depletion of electrons at the surface [131][132][133].…”

Section: Surface Conductivitysupporting

confidence: 63%

“…8(d)). Such a surface electron accumulation was found to be remarkably independent of surface orientation or even bulk polymorph, with a very similar pinning level of the surface Fermi level, and resulting degree of electron accumulation, at the (001) and (111) [135]. In the photoemission spectra, finite spectral intensity can be observed close to the Fermi level in In 2 O 3 (see the magnified spectrum in Fig.…”

Section: Surface Conductivitymentioning

confidence: 77%

“…This enables doped CdO to be rather transparent at visible frequencies, even though the fundamental band gap would seem to be too low to allow this. In some other TCOs such as In 2 O 3 [135,170,192] [194] symmetry dictates that interband transitions between the top valence bands and the bottom conduction band are either dipole forbidden or have only minimal dipole matrix elements, as represented for In 2 O 3 in Fig. 14(a).…”

Section: Transparencymentioning

confidence: 99%

“…Indeed, from direct measurements, measurements of valence band offsets (allowing band alignment relative to the CNL), and theoretical calculations [63,135,[163][164][165][166][167], the CNL has been found to occur above the CBM across the TCOs, as summarized in Fig. 11.…”

Section: Overriding Explanation?mentioning

confidence: 99%

“…Investigating the (100) surface of nearly non-degenerate bixbyite In 2 O 3 films grown by MBE, King et al [134,135] used photoemission spectroscopy to show that the Fermi ‡ For p-type conventional semiconductors, opposite considerations apply, with a positive surface charge from unoccupied donor-like surface states leading to downward band bending. This again leads to a depletion of the majority carriers at the surface.…”

Section: Surface Conductivitymentioning

confidence: 99%

See 4 more Smart Citations

Conductivity in transparent oxide semiconductors

King

Veal

2011

J. Phys.: Condens. Matter

222

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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