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Influence of helium-ion bombardment on the optical properties of ZnO nanorods/p-GaN light emitting diodes
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.ORCID iD: 0000-0001-6235-7038
2011 (English)In: Nanoscale Research Letters, ISSN 1931-7573, Vol. 6, no 628Article in journal (Refereed) Published
Abstract [en]

Light emitting diodes (LEDs) based on zinc oxide (ZnO) nanorods grown by vapor-liquid-solid (VLS) catalytic growth method were irradiated with 2 MeV helium (He+) ions. The fabricated LEDs were irradiated with fluencies of ~ 2×1013 ions/cm2 and ~ 4×1013 ions/cm2. Scanning electron microscopy (SEM) images showed that the morphology of the irradiated samples is not changed. The as-grown and He+ irradiated LEDs showed rectifying behaviour with the same I-V characteristics. Photoluminescence (PL) measurements showed that there is a blue shift of approximately 0.0347 eV and 0.082 eV in the near band emission (free exciton) and green emission of the irradiated ZnO nanorods, respectively. It was also observed that the PL intensity of the near band emission was decreased after irradiation of the samples. The electroluminescence (EL) measurements of the fabricated LEDs showed that there is a blue shift of 0.125 eV in the broad green emission after irradiation and the EL intensity of violet emission approximately centred at 398 nm was nearly disappeared after irradiations. The color rendering properties shows a small decrease in the color rendering indices of 3% after 2 MeV He+ ions irradiation.

Place, publisher, year, edition, pages
SpringerOpen , 2011. Vol. 6, no 628
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-69154DOI: 10.1186/1556-276X-6-628ISI: 000300300100001OAI: oai:DiVA.org:liu-69154DiVA: diva2:424205
Available from: 2011-06-17 Created: 2011-06-17 Last updated: 2014-01-15Bibliographically approved
In thesis
1. Luminescence Properties of ZnO Nanostructures and Their Implementation as White Light Emitting Diodes (LEDs)
Open this publication in new window or tab >>Luminescence Properties of ZnO Nanostructures and Their Implementation as White Light Emitting Diodes (LEDs)
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, luminescence properties of ZnO nanostructures (nanorods, nanotubes, nanowalls and nanoflowers) are investigated by different approaches for possible future application of these nanostructures as white light emitting diodes. ZnO nanostructures were grown by different growth techniques on different p-type substrates. Still it is a challenge for the researchers to produce a stable and reproducible high quality p-type ZnO and this seriously hinders the progress of ZnO homojunction LEDs. Therefore the excellent properties of ZnO can be utilized by constructing heterojunction with other p-type materials.

The first part of the thesis includes paper I-IV. In this part, the luminescence properties of ZnO nanorods grown on different p-type substrates (GaN, 4H-SiC) and different ZnO nanostructures (nanorods, nanotubes, nanoflowers, and nanowalls) grown on the same substrate were investigated. The effect of the post-growth annealing of ZnO nanorods and nanotubes on the deep level emissions and color rendering properties were also investigated.

In paper I, ZnO nanorods were grown on p-type GaN and 4H-SiC substrates by low temperature aqueous chemical growth (ACG) method. The luminescence properties of the fabricated LEDs were investigated at room temperature by electroluminescence (EL) and photoluminescence (PL) measurements and consistency was found between both the measurements. The LEDs showed very bright emission that was a combination of three emission peaks in the violet-blue, green and orange-red regions in the visible spectrum.

In paper II, different ZnO nanostructures (nanorods, nanotubes, nanoflowers, and nanowalls) were grown on p-GaN and the luminescence properties of these nanostructures based LEDs were comparatively investigated by EL and PL measurements. The nanowalls structures were found to be emitting the highest emission in the visible region, while the nanorods have the highest emissions in the UV region due to its good crystal quality. It was also estimated that the ZnO nanowalls structures have strong white light with the highest color rendering index (CRI) of 95 with correlated color temperature (CCT) of 6518 K.

In paper III, we have investigated the origin of the red emissions in ZnO by using post-growth annealing. The ZnO nanotubes were achieved on p-GaN and then annealed in different ambients (argon, air, oxygen and nitrogen) at 600 oC for 30 min. By comparative investigations of EL spectra of the LEDs it was found that more than one deep level defects are involved in the red emission from ZnO nanotubes/p-GaN LEDs. It was concluded that the red emission in ZnO can be attributed to oxygen interstitials (Oi) and oxygen vacancies (Vo) in the range of 620 nm (1.99 eV) to 690 nm (1.79 eV) and 690 nm (1.79 eV) to 750 nm (1.65 eV), respectively.

In paper IV, we have investigated the effect of post-growth annealing on the color rendering properties of ZnO nanorods based LEDs. ZnO nanorods were grown on p-GaN by using ACG method. The as grown nanorods were annealed in nitrogen, oxygen, argon, and air ambients at 600 oC for 30 min. The color rendering indices (CRIs) and correlated color temperatures (CCTs) were estimated from the spectra emitted by the LEDs. It was found that the annealing ambients especially air, oxygen, and nitrogen were found to be very effective. The LEDs based on nanorods annealed in nitrogen ambient, have excellent color rendering properties with CRIs and CCTs of 97 and 2363 K in the forward bias and 98 and 3157 K in the reverse bias.

In the 2nd part of the thesis, the junction temperature of n-ZnO nanorods based LEDs at the built-in potential was modeled and experiments were performed to validate the model. The LEDs were fabricated by ZnO nanorods grown on different p-type substrates (4H-SiC, GaN, and Si) by the ACG method. The model and experimental values of the temperature coefficient of the forward voltage near the built-in potential (~Vo) were compared. It was found that the series resistance has the main contribution in the junction temperature of the fabricated devices.

In the 3rd part of the thesis, the influence of helium (He+) ion irradiation bombardment on luminescence properties of ZnO nanorods based LEDs were investigated. ZnO nanorods were grown by the vapor-liquid-solid (VLS) growth method. The fabricated LEDs were irradiated by using 2 MeV He+ ions with fluencies of ~ 2×1013 ions/cm2 and ~ 4×1013 ions/cm2. It was observed that the He+ ions irradiation affects the near band edge emissions as well as the deep level emissions in ZnO. A blue shift about 0.0347 eV and 0.082 eV was observed in the PL spectra in the near band emission and green emission, respectively. EL measurements also showed a blue shift of 0.125 eV in the broad green emission after irradiation. He+ ion irradiation affects the color rendering properties and decreases the color rendering indices from 92 to 89.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2011. 108 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1378
Keyword
Nanotechnology, Zinc oxide, nanostructures, luminescence, LEDs, color rendering
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-69155 (URN)978-91-7393-139-7 (ISBN)
Public defence
2011-08-26, K2, Kåkenhus, Campus Norrköping, Linköpings universitet, Norrköping, 10:15 (English)
Opponent
Supervisors
Available from: 2011-06-17 Created: 2011-06-17 Last updated: 2014-01-15Bibliographically approved

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