First-Principles Calculations of Co Impurities and Native Defects in ZnO

Oba, Fumiyasu; Yamamoto, Takahisa; Ikuhara, Yuichi; Tanaka, Isao; Adachi, Hirohiko

doi:10.2320/matertrans.43.1439

Cited by 19 publications

(12 citation statements)

References 44 publications

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“…One theoretical investigation proposed the formation of Co Zn -native defects in ZnO under an oxygen-rich atmosphere. 33 The decrease in n e with increasing p͑O 2 ͒ was due to an increase in E d following the generation of deep donor levels. Figure 7͑b͒ shows E d and M s at 10 K in Zn-polar Zn 0.94 Co 0.06 O layers as a function of n e at 300 K. A large M s was observed in the high n e regions supplied from shallow donor levels, while an increase in E d was suppressed following FM ordering with a decrease in n e .…”

Section: Correlation With Electrical and Magnetic Propertiesmentioning

confidence: 96%

Simultaneous control of growth mode and ferromagnetic ordering in Co-doped ZnO layers with Zn polarity

Matsui

Tabata

2007

Phys. Rev. B

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In this paper, we describe a new growth technique realizing the simultaneous control of growth mode and ferromagnetic ordering in Co-doped ZnO layers. Remarkable changes in growth occurred as a result of doping with Co ions. Exposure to O 2 plasma to generate an oxygen-rich atmosphere was indispensable for the fabrication of undoped ZnO layers given stabilization of the negatively charged growing surface in a twodimensional ͑2D͒ mode. In contrast, the 2D mode of Zn 0.94 Co 0.06 O layers was adequately retained in the absence of a plasma source, and was attributable to the covalence provided by the 3d character of Co ions compared with the 4s character of Zn ions. Spontaneous magnetization of Zn 0.94 Co 0.06 O layers was closely correlated with the number of free electrons, which was controlled by the activation energy of donor levels. This was also confirmed for O-polar Zn 0.94 Co 0.06 O layers. Ferromagnetic ͑FM͒ ordering was observed at n e values close to the Mott transition and led to hopping conduction between shallow donor bands. However, levels of p͑O 2 ͒ below 10 −6 mbar that yielded FM ordering generated a pitted surface and led to crystalline deterioration. Given our understanding of the formation mechanism of pits, we applied a periodic oxygen pressure-modulated epitaxy that resulted in the coherent growth of Co-doped ZnO layers with a 2D mode. This specific growth was effective in producing pit-free surface uniformities over large areas that maintained FM ordering.

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Section: Correlation With Electrical and Magnetic Propertiesmentioning

confidence: 96%

Simultaneous control of growth mode and ferromagnetic ordering in Co-doped ZnO layers with Zn polarity

Matsui

Tabata

2007

Phys. Rev. B

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“…For ZnO based varistor materials, Co dopant is known as one of the key additives to obtain/improve non-linear I -V characteristics in ZnO varistor [1,2]. Although Co dopant itself cannot be an acceptor [24,28,29], it has been proposed that Co dopant generate DSB by the stabilization of O 00 i [30,31] or V 00…”

Section: Discussionmentioning

confidence: 99%

Non-linear current–voltage characteristics related to native defects in SrTiO₃ and ZnO bicrystals

Satô

Tanaka

Oba

et al. 2003

Science and Technology of Advanced Materials

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SrTiO 3 and ZnO bicrystals with various types of boundaries were fabricated in order to examine their current -voltage characteristics across single grain boundaries. Their grain boundary structures were also investigated by high-resolution transmission electron microscopy. In Nb-doped SrTiO 3 , electron transport behaviors depend on the type of boundaries. Random type boundaries exhibit highly non-linear current-voltage characteristics, while low angle boundaries show a slight non-linearity. On the contrary, undoped ZnO does not exhibit nonlinear current -voltage characteristics in any type of boundaries including random ones. It is suggested that the differences observed in current-voltage properties between the two systems are mainly due to the difference in the accumulation behavior of acceptor-like native defects at grain boundaries. A clear non-linearity is obtained by means of Co-doping even for the highly coherent S1 boundary in a ZnO bicrystal. This is considered to result from the production of acceptor-like native defects by Co-doping. q

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“…31) An increase in these defects can increase the n-p-n barrier height at the grain-grain boundary interface and lead to an increased barrier to electron transport.…”

Section: Thermoelectric Properties 321 Electronic Transportmentioning

confidence: 99%

Sintering characteristics and thermoelectric properties of Mn–Al co-doped ZnO ceramics

Hoemke

Khan²,

Yoshida³

et al. 2016

J. Ceram. Soc. Japan

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Polycrystalline MnAl co-doped ZnO ceramics were prepared by sintering in air. Increasing Mn dopant concentration led to an increase of the ZnO lattice constants indicating substitution of Mn on the Zn sublattice. A Mn-rich spinel secondary phase was also detected within grains and at grain boundaries. The addition of the Al dopant led to an initial reduction in grain size while the addition of Mn led to an increase in grain size. Thermoelectric property measurements revealed that Al doping led to a large initial increase in electrical conductivity and increasing Mn dopant addition resulted in electrical conductivity reduction. The absolute value of the Seebeck coefficient was largely unaffected at low Mn doping levels; however, an increase was observed for high Mn doping levels. The thermal conductivity showed a marked decrease with increasing Mn concentration, indicating the effectiveness of Mn dopant substitution for Zn to reduce the thermal conductivity by point defect scattering. Overall, the maximum ZT was achieved for the Zn 0.99 Al 0.01 O sample (ZT = 0.07 at 750°C) and increasing Mn doping led to a decrease of ZT due to the increased resistivity caused by alloy scattering and secondary phase formation.

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First-Principles Calculations of Co Impurities and Native Defects in ZnO

Cited by 19 publications

References 44 publications

Simultaneous control of growth mode and ferromagnetic ordering in Co-doped ZnO layers with Zn polarity

Simultaneous control of growth mode and ferromagnetic ordering in Co-doped ZnO layers with Zn polarity

Non-linear current–voltage characteristics related to native defects in SrTiO₃ and ZnO bicrystals

Sintering characteristics and thermoelectric properties of Mn–Al co-doped ZnO ceramics

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First-Principles Calculations of Co Impurities and Native Defects in ZnO

Cited by 19 publications

References 44 publications

Simultaneous control of growth mode and ferromagnetic ordering in Co-doped ZnO layers with Zn polarity

Simultaneous control of growth mode and ferromagnetic ordering in Co-doped ZnO layers with Zn polarity

Non-linear current–voltage characteristics related to native defects in SrTiO3 and ZnO bicrystals

Sintering characteristics and thermoelectric properties of Mn&ndash;Al co-doped ZnO ceramics

Contact Info

Product

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Non-linear current–voltage characteristics related to native defects in SrTiO₃ and ZnO bicrystals

Sintering characteristics and thermoelectric properties of Mn–Al co-doped ZnO ceramics