Hydrogen incorporation and diffusivity in plasma-exposed bulk ZnO

Ip, K.; Overberg, M. E.; Heo, Young‐Woo; Norton, D. P.; Pearton, S. J.; Stutz, C. E.; Luo, B.; Ren, F.; Zavada, J. M.

doi:10.1063/1.1539927

Cited by 202 publications

(118 citation statements)

References 26 publications

(24 reference statements)

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“…While these studies show it to be a shallow donor in TCOs, it is not a priori clear that such species will be stable at elevated temperatures, for example during growth or even some device operating temperatures, where the conductivity of TCOs is known to persist. Indeed, deuterium was observed to diffuse easily in ZnO with an activation energy of only 170 meV [111]. While diffusion of hydrogen into ZnO was seen to lead to an increase both in electron concentration and an associated local vibrational O-H stretching mode observed in infrared spectroscopy [90], both were subsequently substantially reduced by annealing at only 150 • C for 30 mins [96].…”

Section: Stabilitymentioning

confidence: 98%

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: 98%

Conductivity in transparent oxide semiconductors

King

Veal

2011

J. Phys.: Condens. Matter

224

180

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“…The study of the production and recovery process of these defects is therefore very important for a successful doping. There have been a number of studies on the defects induced by ion implantation in ZnO using Rutherford backscattering, 12,13 photoluminescence and cathodoluminescence, 14 deep-level transient spectroscopy, 15 secondary-ion-mass spectrometry, 16 and other electrical characterization methods. 17,18 In addition to these methods, positron annihilation spectroscopy has recently emerged as a powerful tool for the study of vacancy-type defects in semiconductors.…”

Section: Introductionmentioning

confidence: 99%

Production and recovery of defects in phosphorus-implanted ZnO

Chen

Kawasuso

et al. 2004

Journal of Applied Physics

132

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Articles you may be interested inReuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Phosphorus ions were implanted in ZnO single crystals with energies of 50-380 keV having total doses of 4.2ϫ 10 13 -4.2ϫ 10 15 cm −2 . Positron annihilation measurements reveal the introduction of vacancy clusters after implantation. These vacancy clusters grow to a larger size after annealing at a temperature of 600°C. Upon further annealing up to a temperature of 1100°C, the vacancy clusters gradually disappear. Raman-scattering measurements reveal the enhancement of the phonon mode at approximately 575 cm −1 after P + implantation, which is induced by the production of oxygen vacancies ͑V O ͒. These oxygen vacancies are annealed out up to a temperature of 700°C accompanying the agglomeration of vacancy clusters. The light emissions of ZnO are suppressed after implantation. This is due to the competing nonradiative recombination centers introduced by implantation. The recovery of the light emission occurs at temperatures above 600°C. The vacancy-type defects detected by positrons might be part of the nonradiative recombination centers. The Hall measurement indicates an n-type conductivity for the P + -implanted ZnO layer, suggesting that phosphorus is an amphoteric dopant.

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“…However, after annealing at 300°C, the PL intensity of H implanted ZnO decreased by an order of magnitude, suggesting incomplete recovery or passivation of the lattice damage caused by ion implantation. While 300°C is sufficient to allow the implanted H to escape partially from ZnO crystals, 10 it is not sufficient to remove most of the defects formed during ion implantation. This suggests that the decrease in PL intensity for annealed ZnO was due to H loss and the presence of unpassivated defects.…”

mentioning

confidence: 99%

Optical observation of donor-bound excitons in hydrogen-implanted ZnO

Lee

Nastasi

Hamby

et al. 2005

Applied Physics Letters

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The optical and structural properties of H or He implanted ZnO were investigated using low temperature photoluminescence (PL) and infrared spectroscopy (IR). H implantation is shown to influence the relative luminescence intensities of the donor bound excitons, enhancing the 3.361 eV peak, and changing the overall intensity of the PL spectrum. PL from He implanted ZnO is used to demonstrate that implantation damage is partially responsible for the variations observed in the PL of H implanted ZnO. IR spectra show that the increase in the relative intensity of the 3.361 eV peak coincides with an appearance of the H vibrational mode in the ZnO lattice. Our results indicate that the implanted H forms O–H bonds at Zn vacancies, and that it is these defect complexes which give rise to the shallow donors participating in the observed bound-exciton luminescence at 3.361 eV.

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Hydrogen incorporation and diffusivity in plasma-exposed bulk ZnO

Cited by 202 publications

References 26 publications

Conductivity in transparent oxide semiconductors

Conductivity in transparent oxide semiconductors

Production and recovery of defects in phosphorus-implanted ZnO

Optical observation of donor-bound excitons in hydrogen-implanted ZnO

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