An aqueous solution process and subsequent UV treatment for highly transparent conductive ZnO films

Wagata, Hajime; Ohashi, Naoki; Katsumata, Kenji; Segawa, Hiroyo; Wada, Yoshiki; Yoshikawa, Hideki; Ueda, Shigenori; Okada, Kiyoshi; Matsushita, Nobuhiro

doi:10.1039/c2jm33584k

Cited by 37 publications

(36 citation statements)

References 78 publications

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“…2 demonstrates a decrease of the DLS peak intensity from the ND to the 2 week aged and the dried sample. This feature is understood as a result of organic species 14 , defect complexes 17 due to water 15 , or OH groups 13 loosely bound to the NR surface introduced during CBD. These defect species can act as shallow donors, are easily removed after UV exposure 14 , and create a ±10 nm shift in the DLS PL spectrum.…”

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“…This feature is understood as a result of organic species 14 , defect complexes 17 due to water 15 , or OH groups 13 loosely bound to the NR surface introduced during CBD. These defect species can act as shallow donors, are easily removed after UV exposure 14 , and create a ±10 nm shift in the DLS PL spectrum. Therefore, we conclude that drying the sample removes these defect species from the surface lowering, but stabilizing, the PL intensity.…”

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confidence: 99%

“…In a second model, V o is reported to be a deep level state (DLS) and so cannot be a donor state 1 The quality, diameter, and length of the NRs was measured using a Gemini field emission scanning electron microscopy (SEM) Carl Zeiss SUPRATM 25. CBD introduces water based absorbates [13][14][15] , we controlled this parameter by comparing samples as-prepared not dried (ND), dried at 100 o C for 20 min on a hot plate, and left to dry over two weeks. Additionally, we annealed a sample at 600 o C for 30 min in O 2 to understand the role of V o .…”

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confidence: 99%

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Photoluminescence transient study of surface defects in ZnO nanorods grown by chemical bath deposition

Barbagiovanni

Strano

Franzò

et al. 2015

Applied Physics Letters

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Two deep level defects (2.25 and 2.03 eV) associated with oxygen vacancies (V o ) were identified in ZnO nanorods (NRs) grown by low cost chemical bath deposition. A transient behaviour in the photoluminescence (PL) intensity of the two V o states was found to be sensitive to the ambient environment and to NR postgrowth treatment. The largest transient was found in samples dried on a hot plate with a PL intensity decay time, in air only, of 23 and 80 s for the 2.25 and 2.03 eV peaks, respectively. Resistance measurements under UV exposure exhibited a transient behaviour in full agreement with the PL transient indicating a clear role of atmospheric O 2 on the surface defect states. A model for surface defect transient behaviour due to band bending with respect to the Fermi level is proposed. The results have implications for a variety of sensing and photovoltaic applications of ZnO NRs.PACS numbers: 68.43. Fg, 68.43.Tj, 73.20.Hb, 73.20.At Zinc oxide is a wide band gap (∼ 3.2→3.4 eV) ntype semiconductor with a large exciton binding energy (60 meV) and is a promising material for a range of applications 1 . However, studies on low cost ZnO nanostructures (NSs) and thin films are unclear as to the source of n-type conductivity and persistent photoconductivity (PPC), the UV sensing mechanism, and the defect landscape 2,3 . In particular, the correlation between the defect landscape and sensing (whether gas, pH, or UV) responsivity in low cost ZnO NRs is debated. In one model, the neutral oxygen vacancy (V o ) is an n-type donor state 3 , atmospheric O 2 absorbs at this site 2 , and a depletion region forms beneath the surface 4 . UV excitation creates electron-hole pairs, holes migrate to the depletion region and O 2 desorption occurs, thus reducing the depletion region and increasing the conductivity 4,5 . Therefore, the kinetics of O 2 desorption determine the response time of a UV sensor. In a second model, V o is reported to be a deep level state (DLS) The quality, diameter, and length of the NRs was measured using a Gemini field emission scanning electron microscopy (SEM) Carl Zeiss SUPRATM 25. CBD introduces water based absorbates 13-15 , we controlled this parameter by comparing samples as-prepared not dried (ND), dried at 100 o C for 20 min on a hot plate, and left to dry over two weeks. Additionally, we annealed a sample at 600 o C for 30 min in O 2 to understand the role of V o .Resistance measurements were performed under exposure to 364 nm UV light. The samples were biased to force a current of 1 nA between two probes 1 mm apart to extract the resistance. This value was used to avoid compliance in the samples and gave a good overall response under UV exposure. PL measurements were performed by pumping at 1.5 mW the 325 nm line of a He-Cd laser chopped through an acousto-optic modulator at a frequency of 55 Hz. The PL signal was analyzed by a single grating monochromator, detected with a Hamamatsu visible photomultiplier, and recorded with a lock-in am-

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Photoluminescence transient study of surface defects in ZnO nanorods grown by chemical bath deposition

Barbagiovanni

Strano

Franzò

et al. 2015

Applied Physics Letters

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“…15 First, generation of hydrogen and carbon species can be expected by photodecomposition of organic substances, being assumed to play a shallow-donor role. [19][20][21][22] As a result, some electrons were generated, resulting in increased carrier concentration.…”

Section: Al-doped Zno Film With Citrate Ionsmentioning

confidence: 99%

“…23,24 The increased optical bandgap energy is related to the increase of the carrier concentration by UV irradiation, as explained by the Burstein-Moss effect. 19,[25][26][27] Another reason for the decreased resistivity is the Al-ion doping. The amount of Al in the as-deposited film was evaluated by ICPS, confirming the presence of 1.5 ppm Al in the as-deposited film.…”

Section: Al-doped Zno Film With Citrate Ionsmentioning

confidence: 99%

Fabrication of Al-Doped ZnO Film with High Conductivity Induced by Photocatalytic Activity

Hong

Katsumata

Matsushita

2016

Journal of Elec Materi

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We have fabricated Al-doped ZnO films by a spin-spray method, achieving high conductivity by Al-ion doping and photocatalytic activity of the ZnO. The surface morphology of the as-deposited films was varied by changing the Al concentration and addition of citrate ions. As-deposited Al-doped ZnO film without citrate ions showed rod array structure with increasing rod width as the Al concentration was increased. Meanwhile, Al-doped ZnO film deposited with addition of citrate ions changed to exhibit dense and continuous surface morphology with high transmittance of 85%. The lowest resistivity recorded for undoped and Al-doped ZnO film was 2.1 9 10 À2 X cm and 5.9 9 10 À3 X cm, after ultraviolet (UV) irradiation. The reason for the decreased resistivity is thought to be that Al-ion doping and the photocatalytic activity of ZnO contributed to improve the conductivity.

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Chemical Bath Deposition

Fuchs

Romanyuk

Tiwari

2018

Transparent Conductive Materials

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An aqueous solution process and subsequent UV treatment for highly transparent conductive ZnO films

Cited by 37 publications

References 78 publications

Photoluminescence transient study of surface defects in ZnO nanorods grown by chemical bath deposition

Photoluminescence transient study of surface defects in ZnO nanorods grown by chemical bath deposition

Fabrication of Al-Doped ZnO Film with High Conductivity Induced by Photocatalytic Activity

Chemical Bath Deposition

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