Point defects in ZnO

Sokol, Alexey A.; French, Samuel A.; Bromley, Stefan T.; Catlow, C. Richard A.; Dam, Hubertus J. J. van; Sherwood, Paul

doi:10.1039/b607406e

Cited by 160 publications

(142 citation statements)

References 53 publications

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“…A lthough polarons are crucial for optoelectronics, photovoltaics and photochemistry 1 , little is known about polaron lifetimes and binding energies (BEs) [2][3][4] . More information on polaronic states is urgently needed, particularly for enhancing our understanding of photochemistry, where the most promising results are expected to come from well-defined, monocrystalline system, for example, ZnO substrates.…”

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confidence: 99%

Evidence for photogenerated intermediate hole polarons in ZnO

et al. 2015

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Despite their pronounced importance for oxide-based photochemistry, optoelectronics and photovoltaics, only fairly little is known about the polaron lifetimes and binding energies. Polarons represent a crucial intermediate step populated immediately after dissociation of the excitons formed in the primary photoabsorption process. Here we present a novel approach to studying photoexcited polarons in an important photoactive oxide, ZnO, using infrared (IR) reflection-absorption spectroscopy (IRRAS) with a time resolution of 100 ms. For welldefined (10-10) oriented ZnO single-crystal substrates, we observe intense IR absorption bands at around 200 meV exhibiting a pronounced temperature dependence. On the basis of first-principles-based electronic structure calculations, we assign these features to hole polarons of intermediate coupling strength.

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confidence: 99%

Evidence for photogenerated intermediate hole polarons in ZnO

et al. 2015

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“…For ZnO, a much better reproduction of the band structure than the LDA and GGA has been demonstrated using various hybrid functionals, e.g. B3LYP [104], B97-1 [105], PBE0 [44] and HSE [44,83]. The way and amount of the admixture of the non-local exchange differ between hybrid functionals, and the results show some dispersion.…”

Section: Fundamental Properties Of Znomentioning

confidence: 99%

Point defects in ZnO: an approach from first principles

Oba

Choi

Togo

et al. 2011

Science and Technology of Advanced Materials

315

222

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Recent first-principles studies of point defects in ZnO are reviewed with a focus on native defects. Key properties of defects, such as formation energies, donor and acceptor levels, optical transition energies, migration energies and atomic and electronic structure, have been evaluated using various approaches including the local density approximation (LDA) and generalized gradient approximation (GGA) to DFT, LDA + U/GGA + U , hybrid Hartree-Fock density functionals, sX and GW approximation. Results significantly depend on the approximation to exchange correlation, the simulation models for defects and the post-processes to correct shortcomings of the approximation and models. The choice of a proper approach is, therefore, crucial for reliable theoretical predictions. First-principles studies have provided an insight into the energetics and atomic and electronic structures of native point defects and impurities and defect-induced properties of ZnO. Native defects that are relevant to the n-type conductivity and the non-stoichiometry toward the O-deficient side in reduced ZnO have been debated. It is suggested that the O vacancy is responsible for the non-stoichiometry because of its low formation energy under O-poor chemical potential conditions. However, the O vacancy is a very deep donor and cannot be a major source of carrier electrons. The Zn interstitial and anti-site are shallow donors, but these defects are unlikely to form at a high concentration in n-type ZnO under thermal equilibrium. Therefore, the n-type conductivity is attributed to other sources such as residual impurities including H impurities with several atomic configurations, a metastable shallow donor state of the O vacancy, and defect complexes involving the Zn interstitial. Among the native acceptor-type defects, the Zn vacancy is dominant. It is a deep acceptor and cannot produce a high concentration of holes. The O interstitial and anti-site are high in formation energy and/or are electrically inactive and, hence, are unlikely to play essential roles in electrical properties. Overall defect energetics suggests a preference for the native donor-type defects over acceptor-type defects in ZnO. The O vacancy, Zn interstitial and Zn anti-site have very low formation energies when the Fermi level is low. Therefore, these defects are expected to be sources of a strong hole compensation in p-type ZnO. For the n-type doping, the compensation of carrier electrons by the native acceptor-type defects can be mostly suppressed when O-poor chemical potential conditions, i.e. low O partial pressure conditions, are chosen during crystal growth and/or doping.

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“…In other words, in thermal equilibrium, the F + centre will only be metastable: for any equilibrium position of the Fermi energy within the band gap, the defect state will exist either as an F or The energies for Schottky pair formation (intrinsic ionic disorder involving noninteracting site vacancies) are listed in table 2. Both materials exhibit a preference for charged Schottky formation owing to the beneficial electron transfer between donor and acceptor states; however, the charge state preferences differ in the two cases: PbS favours doubly charged (fully ionized) disorder, while Pb 3 (C 6 S 6 ) favours the single ionized Schottky disorder as the defect level of V , 3.45 eV in ZnO (Sokol et al 2007;Catlow et al 2008), 3.67 eV in SnO 2 (Godinho et al 2009), and 4.7 eV in GaN . For all defect reactions, the formation energies are substantially higher in the hybrid materials, which would suggest that their concentrations will be much lower: to produce semiconducting samples, it may be necessary to extrinsically dope these materials.…”

Section: (C) Defect Chemistrymentioning

confidence: 99%

Effects of reduced dimensionality on the electronic structure and defect chemistry of semiconducting hybrid organic–inorganic PbS solids

Walsh

2011

Proc. R. Soc. A.

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The combination of inorganic and organic frameworks to produce crystalline hybrid semiconductors offers a pathway for obtaining novel photovoltaic and optoelectronic materials. Taking an archetypal binary semiconductor, PbS (galena), we investigate the electronic effects of the reduced dimensionality in the PbS framework on transition from bulk PbS to three-dimensional and one-dimensional hybrid inorganic-organic networks. Analysis of density functional theory calculations reveals the substantial contribution of the organic (benzenehexathiol derivates) to the band-edge states. Implications for intrinsic defect formation and potential application in solar cell devices are discussed, as well as future design pathways for engineering the electronic properties of this new class of hybrid metal-organic framework.

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Point defects in ZnO

Cited by 160 publications

References 53 publications

Evidence for photogenerated intermediate hole polarons in ZnO

Evidence for photogenerated intermediate hole polarons in ZnO

Point defects in ZnO: an approach from first principles

Effects of reduced dimensionality on the electronic structure and defect chemistry of semiconducting hybrid organic–inorganic PbS solids

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