Zinc oxide as a model transparent conducting oxide: A theoretical and experimental study of the impact of hydroxylation, vacancies, interstitials, and extrinsic doping on the electronic properties of the Polar ZnO (0002) surface

Hong Li, Laura K. Schirra, Jaewon Shim, Hyeunseok Cheun, Bernard Kippelen, Oliver L.A. Monti, Jean-Luc Bredas*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

93 Scopus citations

Abstract

The technology-relevant zinc-terminated zinc oxide (0002) polar surface has been studied at the density-functional theory level using both Perdew-Burke-Ernzerhof (PBE) and hybrid Heyd-Scuseria-Ernzerhof (HSE06) functionals. We have considered a number of surface conditions to better understand the impact of surface hydroxylation and intrinsic and extrinsic surface defects, including zinc vacancies, oxygen vacancies, zinc interstitials, and aluminum dopants on the surface electronic properties. Our calculations point to large variations in surface work function and energy band gap as a function of the surface model; these variations can be attributed to changes in surface charge carrier density and to additional surface states induced by the defects. The calculated shifts in O(1s) core-level binding energy of the surface oxygens in different bonding configurations are in good agreement with experimental X-ray photoelectron spectroscopy data and point to the presence of two distinct OH-species on the ZnO surface. Our results also show that the electron-compensation centers induced by zinc vacancies can be stabilized by intrinsic and/or extrinsic n-type doping near the surface; such n-type doping can lead to better performance of organic opto-electronic devices in which zinc oxide is used as an electron-selective interlayer.

Original languageEnglish (US)
Pages (from-to)3044-3055
Number of pages12
JournalChemistry of Materials
Volume24
Issue number15
DOIs
StatePublished - Aug 14 2012

Keywords

  • DFT slab calculations
  • conducting oxide
  • surface defects
  • work-function determination
  • zinc oxide

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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