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Forward- and reverse-biased electroluminescence behavior of chemically fabricated ZnO nanotubes/GaN interface
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 Science and Technology. Linköping University, The Institute of Technology.
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
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2011 (English)In: SEMICONDUCTOR SCIENCE AND TECHNOLOGY, ISSN 0268-1242, Vol. 26, no 7, 075003- p.Article in journal (Refereed) Published
Abstract [en]

Electroluminescence characteristics of an n-ZnO nanotubes/p-GaN heterostructure light-emitting diode (LED) have been investigated at forward and reverse bias. Distinctly different emission spectra have been observed and the location of the recombination of electron-hole is analyzed under both configurations. The forward-biased emission spectrum shows two peaks centered at around 450 and 560 nm, while the reverse-biased spectrum exhibits a single emission peak at 650 nm. By comparing the current transport mechanisms, it is suggested that the violet-blue emission peak (450 nm) observed only under forward bias is originating from the heterojunction of the ZnO nanotubes/p-GaN LED. The influence on the emission intensity of the device with the increase in temperature at constant current is studied in the range from 25 to 65 degrees C, to check its compatibility for practical applications and under harsh conditions.

Place, publisher, year, edition, pages
Iop Publishing Ltd , 2011. Vol. 26, no 7, 075003- p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-67962DOI: 10.1088/0268-1242/26/7/075003ISI: 000289554400004OAI: oai:DiVA.org:liu-67962DiVA: diva2:414742
Available from: 2011-05-04 Created: 2011-05-04 Last updated: 2014-01-15
In thesis
1. Chemically Synthesized ZnO Nanostructures: Realization of White Optoelectronic Devices with High CRI Values
Open this publication in new window or tab >>Chemically Synthesized ZnO Nanostructures: Realization of White Optoelectronic Devices with High CRI Values
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Recently in a couple of decades, nanotechnology and nanoscience are becoming wide spread fields of research due to the revolutionary advances in the manufacturing processes which enable the realization of infinitesimally modest nanodevices holding a huge variety of fascinating properties and applications. Besides various functional materials, ZnO has captivated interests for a variety of applications in electronics and optoelectronics owing to its unique characteristics; such as, direct wide band gap, large exciton binding energy, semiconducting, photonic, and piezoelectric properties. A distinguished capability of the ZnO material is the effortless synthesis of nanoscale structures with enormous assortments in their morphological and dimensional aspects. Regardless the significant developments in the fabrication of ZnO based homojunction optoelectronic nanodevices, the stable and reproducible p-type conductivity of ZnO material is still a challenge which is one of the paramount factors of the increasing interest for fabrication of heterojunction of ZnO nanostructures with other mainstream ptype semiconductors, such as Si, GaN, and organic materials.

Herein, ZnO nanorods, nanotubes and nanoflowers have been synthesized by solution-based methodology at low temperature (<100 ˚C) and a thorough study on the applications of ZnO nanostructures as white light emitting diodes (LEDs) has been perceived. At the outset, ZnO nanotubes have been synthesized by the trimming of aqueous chemically grown ZnO nanorods with 100% yield and their comparative optical properties have been explored through photoluminescence study, and a profound enhancement in ultraviolet and visible emission is observed (paper I). ZnO nanotubes are further exploited for its promising application as an optoelectronic device. Pure white light emission is observed from the ZnO nanotubes/p-GaN based LED. To analyze the location of the recombination of electron–hole and current transport mechanisms, the EL characteristics of n-ZnO nanotubes/p-GaN heterostructure LED have been investigated under forward and reverse bias. The origin of distinctly different EL peaks under both configurations has been suggested and the influence of increasing values of temperature on the device characteristics is also studied under fixed applied current, in order to check its performance under harsh conditions and for practical  applications (paper II-III). Moreover, it is observed that ZnO-nanotubes/GaN heterostructure LED has an ability to produce an environmentally benign alternative of traditional lighting sources with high color rendering index (CRI) of 96 (paper IV). On the basis of EL, cathodoluminescence and transmission electron microscopy investigations; a robust correspondence has been established between the formation of radiative surface defect states in the nanotubes and the pure cool white light with appropriate color temperature. In paper V, a miniaturized white LED has been developed using Au/n-ZnO nanorods integrated on a glass pipette (having a sharp cylindrical tip with the diameter of 700 nm) which exhibits a broad EL band emission covering the whole visible spectrum range and a CRI value of 73. Besides one-dimensional ZnO nanostructures (nanorods and nanotubes), three-dimensional ZnO dahlia-flower nanoarchitectures have also been fabricated at room temperature relying on natural oxidation based aqueous chemically synthetic approach (paper VI).  Glycineassisted multi-oriented ZnO nanoflowers with highly large surface area to volume ratio have been synthesized on Zn foil substrate through the self-assembly of thin nano-petals as building blocks and polar surfaces of ZnO have been anticipated to be  stabilized through the adsorption of reactive hydroxyl and amide functions of glycine.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 62 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1466
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-80634 (URN)978-91-7519-833-0 (ISBN)
Public defence
2012-09-14, K3, Kåkenhus, Campus Norrköping, Linköpings universitet, Norrköping, 10:15 (English)
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Available from: 2012-08-28 Created: 2012-08-28 Last updated: 2014-01-15Bibliographically approved

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