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Chemically Synthesized ZnO Nanostructures: Realization of White Optoelectronic Devices with High CRI Values
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
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: urn:nbn:se:liu:diva-80634ISBN: 978-91-7519-833-0 (print)OAI: oai:DiVA.org:liu-80634DiVA: diva2:547481
Public defence
2012-09-14, K3, Kåkenhus, Campus Norrköping, Linköpings universitet, Norrköping, 10:15 (English)
Opponent
Supervisors
Available from: 2012-08-28 Created: 2012-08-28 Last updated: 2014-01-15Bibliographically approved
List of papers
1. Trimming of aqueous chemically grown ZnO nanorods into ZnO nanotubes and their comparative optical properties
Open this publication in new window or tab >>Trimming of aqueous chemically grown ZnO nanorods into ZnO nanotubes and their comparative optical properties
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2009 (English)In: APPLIED PHYSICS LETTERS, ISSN 0003-6951, Vol. 95, no 7, 073114- p.Article in journal (Refereed) Published
Abstract [en]

Highly oriented ZnO nanotubes were fabricated on a silicon substrate by aqueous chemical growth at low temperature (andlt; 100 degrees C) by trimming of ZnO nanorods. The yield of nanotubes in the sample was 100%. Photoluminescence spectroscopy of the nanotubes reveals an enhanced and broadened ultraviolet (UV) emission peak, compared with the initial nanorods. This effect is attributed to whispering gallery mode resonance. In addition, a redshift of the UV emission peak is also observed. Enhancement in the deep defect band emission in the nanotubes compared to nanorods was also manifested as a result of the increased surface area.

Keyword
crystal growth from solution, II-VI semiconductors, nanofabrication, red shift, semiconductor growth, semiconductor nanotubes, whispering gallery modes, wide band gap semiconductors, zinc compounds
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-20618 (URN)10.1063/1.3211124 (DOI)
Available from: 2009-09-16 Created: 2009-09-15 Last updated: 2015-03-09
2. White Electroluminescence Using ZnO Nanotubes/GaN Heterostructure Light-Emitting Diode
Open this publication in new window or tab >>White Electroluminescence Using ZnO Nanotubes/GaN Heterostructure Light-Emitting Diode
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2010 (English)In: NANOSCALE RESEARCH LETTERS, ISSN 1931-7573, Vol. 5, no 6, 957-960 p.Article in journal (Refereed) Published
Abstract [en]

We report the fabrication of heterostructure white light-emitting diode (LED) comprised of n-ZnO nanotubes (NTs) aqueous chemically synthesized on p-GaN substrate. Room temperature electroluminescence (EL) of the LED demonstrates strong broadband white emission spectrum consisting of predominating peak centred at 560 nm and relatively weak violet-blue emission peak at 450 nm under forward bias. The broadband EL emission covering the whole visible spectrum has been attributed to the large surface area and high surface states of ZnO NTs produced during the etching process. In addition, comparison of the EL emission colour quality shows that ZnO nanotubes have much better quality than that of the ZnO nanorods. The colour-rendering index of the white light obtained from the nanotubes was 87, while the nanorods-based LED emit yellowish colour.

Place, publisher, year, edition, pages
Springer Science Business Media, 2010
Keyword
ZnO nanotubes, Light-emitting diodes, Electroluminescence, Lightning, White light sources
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-57167 (URN)10.1007/s11671-010-9588-z (DOI)000278096000008 ()
Available from: 2010-06-11 Created: 2010-06-11 Last updated: 2014-09-25
3. Forward- and reverse-biased electroluminescence behavior of chemically fabricated ZnO nanotubes/GaN interface
Open this publication in new window or tab >>Forward- and reverse-biased electroluminescence behavior of chemically fabricated ZnO nanotubes/GaN interface
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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
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-67962 (URN)10.1088/0268-1242/26/7/075003 (DOI)000289554400004 ()
Available from: 2011-05-04 Created: 2011-05-04 Last updated: 2014-01-15
4. The correlation between radiative surface defect states and high color rendering index from ZnO nanotubes
Open this publication in new window or tab >>The correlation between radiative surface defect states and high color rendering index from ZnO nanotubes
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2011 (English)In: Nanoscale Research Letters, ISSN 1931-7573, E-ISSN 1556-276X, Vol. 6, no 513Article in journal (Refereed) Published
Abstract [en]

Combined surface, structural and opto-electrical investigations are drawn from the chemically fashioned ZnO nanotubes and its heterostructure with p-GaN film. A strong correlation has been found between the formation of radiative surface defect states in the nanotubes and the pure cool white light possessing averaged eight color rendering index value of 96 with appropriate color temperature. Highly important deep-red color index value has been realized andgt; 95 which has the capability to render and reproduce natural and vivid colors accurately. Diverse types of deep defect states and their relative contribution to the corresponding wavelengths in the broad emission band is suggested.

Place, publisher, year, edition, pages
SpringerOpen, 2011
Keyword
ZnO nanotubes, ZnO/GaN heterostructure, radiative surface defects, color rendering index, R9 color indexed
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-72037 (URN)10.1186/1556-276X-6-513 (DOI)000296257300001 ()
Available from: 2011-11-11 Created: 2011-11-11 Last updated: 2017-12-08
5. Biomimetically Influenced Synthesis of ZnO Dahlia-Flower Shaped Nanoarchitectures
Open this publication in new window or tab >>Biomimetically Influenced Synthesis of ZnO Dahlia-Flower Shaped Nanoarchitectures
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Three dimensional ZnO dahlia-flower nanoarchitectures have been engineered at room temperature relying on natural oxidation based aqueous chemical synthetic approach. Glycine abetted multicomponent isotropic morphology has been synthesized through the conglomeration of thin nanopetals as building blocks with highly large surface area to volume ratio. Multi-oriented ZnO crystal structure has been achieved by stabilizing its polar surfaces through the adsorption of reactive hydroxyl and amide functions of glycine, exemplifying good corroboration towards x-rays diffraction and Fourier transform infrared ratiocinations.

Keyword
Zinc Oxide, Glycine, Nanoflowers, FTIR, Aqueous Chemical Synthetic Technique
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-80632 (URN)
Available from: 2012-08-28 Created: 2012-08-28 Last updated: 2014-01-15Bibliographically approved
6. Miniaturization of White Light Emitting Diode on the Borosilicate Glass Pipette
Open this publication in new window or tab >>Miniaturization of White Light Emitting Diode on the Borosilicate Glass Pipette
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We present the miniaturization of the white light emitting diode on the borosilicate glass pipette’s tip with the diameter of ~700 nm. Zinc oxide nanowires with the average diameter and length of ~80 nm and ~1.5 μm, respectively, have been chemically synthesized and characterized to investigate the surface morphology, chemical composition and the crystalline nature of the nanoscale structure. The emission capabilities and the color qualities of the broad band emission spectrum from the heterostructure nanodevice have been investigated from electroluminescence measurements and color rendering index calculations.

Keyword
Zinc Oxide, White light emitting diodes, Schottky diode, Transmission Electron Microscopy, Color Rendering Index
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-80631 (URN)
Available from: 2012-08-28 Created: 2012-08-28 Last updated: 2014-01-15Bibliographically approved

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