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Fabrication and Characterization of ZnO Nanorods Based Intrinsic White Light Emitting Diodes (LEDs)
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

ZnO material based hetero-junctions are a potential candidate for the design andrealization of intrinsic white light emitting devices (WLEDs) due to several advantages overthe nitride based material system. During the last few years the lack of a reliable andreproducible p-type doping in ZnO material with sufficiently high conductivity and carrierconcentration has initiated an alternative approach to grow n-ZnO nanorods (NRs) on other ptypeinorganic and organic substrates. This thesis deals with ZnO NRs-hetero-junctions basedintrinsic WLEDs grown on p-SiC, n-SiC and p-type polymers. The NRs were grown by thelow temperature aqueous chemical growth (ACG) and the high temperature vapor liquid solid(VLS) method. The structural, electrical and optical properties of these WLEDs wereinvestigated and analyzed by means of scanning electron microscope (SEM), current voltage(I-V), photoluminescence (PL), cathodoluminescence (CL), electroluminescence (EL) anddeep level transient spectroscopy (DLTS). Room temperature (RT) PL spectra of ZnOtypically exhibit one sharp UV peak and possibly one or two broad deep level emissions(DLE) due to deep level defects in the bandgap. For obtaining detailed information about thephysical origin, growth dependence of optically active defects and their spatial distribution,especially to study the re-absorption of the UV in hetero-junction WLEDs structure depthresolved CL spectroscopy, is performed. At room temperature the CL intensity of the DLEband is increased with the increase of the electron beam penetration depth due to the increaseof the defect concentration at the ZnO NRs/substrate interface. The intensity ratio of the DLEto the UV emission, which is very useful in exploring the origin of the deep level emissionand the distribution of the recombination centers, is monitored. It was found that the deepcenters are distributed exponentially along the ZnO NRs and that there are more deep defectsat the root of ZnO NRs compared to the upper part. The RT-EL spectra of WLEDs illustrateemission band covering the whole visible range from 420 nm and up to 800 nm. The whitelightcomponents are distinguished using a Gaussian function and the components were foundto be violet, blue, green, orange and red emission lines. The origin of these emission lines wasfurther identified. Color coordinates measurement of the WLEDs reveals that the emitted lighthas a white impression. The color rendering index (CRI) and the correlated color temperature(CCT) of the fabricated WLEDs were calculated to be 80-92 and 3300-4200 K, respectively.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2011. , 68 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1401
Keyword [en]
Zinc Oxide nanorods, White light emitting diode, Photoluminescence, Cathodoluminescence, Electroluminescence, Deep level transient spectroscopy (DLTS)
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-71829ISBN: 978-91-7393-054-3 (print)OAI: oai:DiVA.org:liu-71829DiVA: diva2:454302
Public defence
2011-11-11, K3, Kåkenhus, Campus Norrköping, Linköpings universitet, Norrköping, 10:15 (English)
Opponent
Supervisors
Available from: 2011-11-07 Created: 2011-11-07 Last updated: 2014-01-15Bibliographically approved
List of papers
1. Study of Radiative Defects Using Current-Voltage Characteristics in ZnO Rods Catalytically Grown on 4H-p-SiC
Open this publication in new window or tab >>Study of Radiative Defects Using Current-Voltage Characteristics in ZnO Rods Catalytically Grown on 4H-p-SiC
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2010 (English)In: Journal of Nanomaterials, Vol. 2010, no 817201Article in journal (Refereed) Published
Abstract [en]

High-quality ZnO rods were grown by the vapour-liquid-solid (VLS) technique on 4H-p-SiC substrate. The current transport mechanisms of the diodes at room temperature (RT) have been explained in term of the space-charge-limited current model based on the energy band diagram of ZnO rods/4H-p-SiC heterostructure. The tunneling mechanism via deep-level states was found to be the main conduction process at low-applied voltage but at trap-filled limit voltage VTFL all traps are filled and the space-charge-limited current conduction dominated the current transport. From the RT current voltage measurements, the energy of the deep level trap and the trap concentration were obtained as ∼0.24±0.02 eV and 4.4×1018cm−3, respectively. The deep level states observed correspond to zinc interstitial (Zni ), responsible for the violet emission.

Place, publisher, year, edition, pages
Hindawi, 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-67326 (URN)10.1155/2010/817201 (DOI)
Note
Original Publication: Nargis Bano, I. Hussain, Omer Nur, Magnus Willander and P. Klason, Study of Radiative Defects Using Current-Voltage Characteristics in ZnO Rods Catalytically Grown on 4H-p-SiC, 2010, Journal of Nanomaterials, (2010), 817201. http://dx.doi.org/10.1155/2010/817201 Licensee: Hindawi Publishing Corporation http://www.hindawi.com/ Available from: 2011-04-08 Created: 2011-04-08 Last updated: 2014-01-15
2. Study of luminescent centers in ZnO nanorods catalytically grown on 4H-p-SiC
Open this publication in new window or tab >>Study of luminescent centers in ZnO nanorods catalytically grown on 4H-p-SiC
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2009 (English)In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 24, no 12, 125015- p.Article in journal (Refereed) Published
Abstract [en]

High-quality ZnO nanorods (NRs) were grown by the vapor-liquid-solid (VLS) technique on 4H-p-SiC substrates. Heterojunction light emitting diodes (LEDs) were fabricated. Electrical characterization including deep level transient spectroscopy (DLTS) complemented by photoluminescence (PL) is used to characterize the heterojunction LEDs. In contrast to previously published results on n-ZnO thin films on p-SiC, we found that the dominant emission is originating from the ZnO NRs. Three luminescence lines have been observed; these are associated with blue (465 nm) and violet (446 nm) emission lines from ZnO NRs emitted by direct transition/recombination of carriers from the conduction band to a zinc vacancy (V-Zn) radiative center and from a zinc interstitial (Zn-i) radiative center to the valance band. The third green-yellow (575 nm) spectral line is emitted due to a transition of carriers from Zn-i to V-Zn. The superposition of these lines led to the observation of strong white light which appears as a wide band in the room temperature PL.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-52416 (URN)10.1088/0268-1242/24/12/125015 (DOI)
Note
Original Publication: Nargis Bano, I Hussain, Omer Nour, Magnus Willander, P Klason and Anne Henry, Study of luminescent centers in ZnO nanorods catalytically grown on 4H-p-SiC, 2009, SEMICONDUCTOR SCIENCE AND TECHNOLOGY, (24), 12, 125015. http://dx.doi.org/10.1088/0268-1242/24/12/125015 Copyright: Iop Publishing Ltd http://www.iop.org/ Available from: 2010-01-11 Created: 2009-12-18 Last updated: 2017-12-12Bibliographically approved
3. Depth-resolved cathodoluminescence study of zinc oxide nanorods catalytically grown on p-type 4H-SiC
Open this publication in new window or tab >>Depth-resolved cathodoluminescence study of zinc oxide nanorods catalytically grown on p-type 4H-SiC
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2010 (English)In: Journal of Luminescence, ISSN 0022-2313, E-ISSN 1872-7883, Vol. 130, no 6, 963-968 p.Article in journal (Refereed) Published
Abstract [en]

Optical properties of ZnO nanorods (NRs) grown by vapour-liquid-solid (VLS) technique on 4H-p-SiC substrates were probed by cathodoluminescence (CL) measurements at room temperature and at 5 K complemented with electroluminescence. At room temperature the CL spectra for defect related emission intensity was enhanced with the electron beam penetration depth. We observed a variation in defect related green emission along the nanorod axis. This indicates a relatively poor structural quality near the interface between ZnO NRs and p-SiC substrate. We associate the green emission with oxygen vacancies. Analysis of the low-temperature (5 K) emission spectra in the UV region suggests that the synthesized nanorods contain shallow donors and acceptors.

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam., 2010
Keyword
ZnO nanorods, Cathodoluminescence, Deep level luminescence
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-56299 (URN)10.1016/j.jlumin.2010.01.006 (DOI)000276916300008 ()
Note
Original Publication: Nargis Bano, I Hussain, Omer Nour, Magnus Willander, Qamar Ul Wahab, Anne Henry, H S Kwack, D Le Si Dang, Depth-resolved cathodoluminescence study of zinc oxide nanorods catalytically grown on p-type 4H-SiC, 2010, JOURNAL OF LUMINESCENCE, (130), 6, 963-968. http://dx.doi.org/10.1016/j.jlumin.2010.01.006 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2010-05-07 Created: 2010-05-07 Last updated: 2017-12-12Bibliographically approved
4. Study of Au/ZnO nanorods Schottky light-emitting diodes grown by low-temperature aqueous chemical method
Open this publication in new window or tab >>Study of Au/ZnO nanorods Schottky light-emitting diodes grown by low-temperature aqueous chemical method
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2010 (English)In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 100, no 2, 467-472 p.Article in journal (Refereed) Published
Abstract [en]

High quality vertically aligned ZnO nanorods (NRs) were grown by low-temperature aqueous chemical technique on 4H-n-SiC substrates. Schottky light-emitting diodes (LEDs) were fabricated. The current-voltage (I-V) characteristics of Schottky diodes reveal good rectifying behavior. Optical properties of the ZnO nanorods (NRs) were probed by cathodoluminescence (CL) measurements at room temperature complemented with electroluminescence (EL). The room-temperature CL spectra of the ZnO NRs exhibit near band edge (NBE) emission as well as strong deep level emission (DLE) centered at 690 nm. At room temperature the CL spectra intensity of the DLE was enhanced with the increase of the electron beam penetration depth due to the increase of defect concentration at the interface and due to the conversion of self-absorbed UV emission. We observed a variation in the DLE along the nanorod depth. This indicates a relatively lower structural quality near the interface between ZnO NRs and n-SiC substrate. The room-temperature CL spectra of SiC show very weak emission, which confirms that most of the DLE is originating from the ZnO NRs, and SiC has a minute contribution to the emission.

Place, publisher, year, edition, pages
Springer Science Business Media, 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-58660 (URN)10.1007/s00339-010-5722-0 (DOI)000280556600024 ()
Available from: 2010-08-22 Created: 2010-08-20 Last updated: 2017-12-12Bibliographically approved
5. ZnO-organic hybrid white light emitting diodes grown on flexible plastic using low temperature aqueous chemical method
Open this publication in new window or tab >>ZnO-organic hybrid white light emitting diodes grown on flexible plastic using low temperature aqueous chemical method
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2010 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 4, 043103- p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate white light luminescence from ZnO-organic hybrid light emitting diodes grown at 90 degrees C on flexible plastic substrate by aqueous chemical growth. The configuration used for the ZnO-organic hybrid white light emitting diodes (WLEDs) consists of a layer of poly (9, 9-dioctylfluorene) (PFO) on poly (3, 4-ethylenedioxythiophene) poly (styrenesulfonate) coated plastic with top ZnO nanorods. Structural, electrical, and optical properties of these WLEDs were measured and analyzed. Room temperature electroluminescence spectrum reveals a broad emission band covering the range from 420 to 750 nm. In order to distinguish the white light components and contribution of the PFO layer we used a Gaussian function to simulate the experimental data. Color coordinates measurement of the WLED reveals that the emitted light has a white impression. The color rendering index and correlated color temperature of the WLED were calculated to be 68 and 5800 K, respectively.

Place, publisher, year, edition, pages
American Institute of Physics, 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-60234 (URN)10.1063/1.3475473 (DOI)000281857100016 ()
Note
Original Publication: Nargis Bano, Siama Zaman, A Zainelabdin, S Hussain, I Hussain, Omer Nour and Magnus Willander, ZnO-organic hybrid white light emitting diodes grown on flexible plastic using low temperature aqueous chemical method, 2010, JOURNAL OF APPLIED PHYSICS, (108), 4, 043103. http://dx.doi.org/10.1063/1.3475473 Copyright: American Institute of Physics http://www.aip.org/ Available from: 2010-10-08 Created: 2010-10-08 Last updated: 2017-12-12Bibliographically approved
6. Study of intrinsic white light emission and its components from ZnO-nanorods/p-polymer hybrid junctions grown on glass substrates
Open this publication in new window or tab >>Study of intrinsic white light emission and its components from ZnO-nanorods/p-polymer hybrid junctions grown on glass substrates
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2011 (English)In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 46, no 23, 7437-7442 p.Article in journal (Refereed) Published
Abstract [en]

We report white-light luminescence from ZnO-organic hybrid light emitting diodes grown on glass substrate by low temperature aqueous chemical growth. The configuration used for the hybrid white light emitting diodes (HWLEDs) consists of two-layers of polymers (PEDOT:PSS/PFO) on glass with top ZnO nanorods. Electroluminescence spectra of the HWLEDs demonstrate the combination of emission bands arising from the radiative recombination in polymer and ZnO nanorods. In order to distinguish emission bands we used a Gaussian function to simulate the experimental data. The emitted white light was found to be the superposition of a blue line at 454 nm, a green emission at 540 nm, orange line at 617 nm, and finally a red emission at 680 nm. The transitions causing these emissions are identified and discussed in terms of the energy band diagram of the hybrid junction. Color coordinates measurement of the WLED reveals that the emitted light has a white impression with 70 color rendering index and correlated color temperature 5500 K. Comparison between ITO and aluminum top contacts and its influence on the emitted intensity is also discussed.

Place, publisher, year, edition, pages
Springer Verlag (Germany), 2011
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-71543 (URN)10.1007/s10853-011-5708-0 (DOI)000295179700011 ()
Available from: 2011-10-21 Created: 2011-10-21 Last updated: 2017-12-08Bibliographically approved
7. Study of the Distribution of Radiative Defects and Reabsorption of the UV in ZnO Nanorods-Organic Hybrid White Light Emitting Diodes (LEDs)
Open this publication in new window or tab >>Study of the Distribution of Radiative Defects and Reabsorption of the UV in ZnO Nanorods-Organic Hybrid White Light Emitting Diodes (LEDs)
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2011 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 4, no 7, 1260-1270 p.Article in journal (Refereed) Published
Abstract [en]

In this study, the low temperature aqueous chemical growth (ACG) method was employed to synthesized ZnO nanorods to process-organic hybrid white light emitting diodes (LEDs) on glass substrate. Electroluminescence spectra of the hybrid white LEDs demonstrate the combination of emission bands arising from radiative recombination of the organic and ZnO nanorods (NRs). Depth resolved luminescence was used for probing the nature and spatial distribution of radiative defects, especially to study the re-absorption of ultraviolet (UV) in this hybrid white LEDs structure. At room temperature the cathodoluminescence (CL) spectra intensity of the deep band emission (DBE) is increased with the increase of the electron beam penetration depth due to the increase of defect concentration at the ZnO NRs/Polyfluorene (PFO) interface and probably due to internal absorption of the UV. A strong dependency between the intensity ratio of the UV to the DBE bands and the spatial distribution of the radiative defects in ZnO NRs has been found. The comparison of the CL spectra from the PFO and the ZnO NRs demonstrate that PFO has a very weak violet-blue emission band, which confirms that most of the white emission components originate from the ZnO NRs.

Place, publisher, year, edition, pages
Basel, Switzerland: MDPI, 2011
Keyword
ZnO, yousuf soomro, LEDs
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-69643 (URN)10.3390/ma4071260 (DOI)000298245500006 ()
Projects
ZnO semiconductor
Available from: 2011-08-12 Created: 2011-07-08 Last updated: 2017-12-11Bibliographically approved

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