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Annealing effect on the electrical and optical properties of Au/n-ZnO NWs Schottky diodes white LEDs
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
Ecospark AB, Sweden .
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
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2013 (English)In: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 62, 200-206 p.Article in journal (Refereed) Published
Abstract [en]

We report the post-growth heat treatment effect on the electrical and the optical properties of hydrothermally grown zinc oxide (ZnO) nanowires (NWs) Schottky white light emitting diodes (LEDs). It was found that there is a changed in the electroluminescence (EL) spectrum when post growth annealing process was performed at 600 degrees C under nitrogen, oxygen and argon ambients. The EL spectrum for LEDs based on the as grown NWs show three bands red, green and blue centered at 724, 518 and 450 nm respectively. All devices based on ZnO NWs annealed in oxygen (O-2), nitrogen (N-2) and argon (Ar) ambient show blue shift in the violet and the red emissions whereas a red shift is observed in the green emission compared to the as grown NWs based device. The color rendering index (CRI) and the correlated color temperature (CCT) of all LEDs were calculated to be in the range 78-91 and 2753-5122 K, respectively. These results indicate that light from the LEDs can be tuned from cold white light to warm white light by post growth annealing.

Place, publisher, year, edition, pages
Elsevier , 2013. Vol. 62, 200-206 p.
Keyword [en]
ZnO nanowires, Schottky diodes, Post growth annealing, Electroluminescence
National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-100481DOI: 10.1016/j.spmi.2013.07.014ISI: 000325588700022OAI: diva2:662971
Available from: 2013-11-08 Created: 2013-11-08 Last updated: 2014-04-28
In thesis
1. Fabrication and Characterization of Zinc Oxide Nanostructures for Piezoelectric, Mechanical and Electrical Applications
Open this publication in new window or tab >>Fabrication and Characterization of Zinc Oxide Nanostructures for Piezoelectric, Mechanical and Electrical Applications
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nanotechnology, the science of manipulating materials on an atomic or molecular scale is one of the fastest growing areas of research and technology. Nanotechnology has a vast range of applications in medicine, electronics, biomaterials and energy production. New developments in nanotechnology are growing all the time. In the near future, nanotechnology is expected to be a mature industry, with countless mainstream products.

Zinc Oxide (ZnO) is an important and optimal material in electronic and photonic applications due to its important properties like direct band gap (3.3 eV) semiconductor with large exciton binding energy (60 meV) which can provide more efficient excitonic emission even at room temperature. Beside that noncentrosymmetric property of ZnO makes it an ideal piezoelectric material. Various onedimensional ZnO nanostructures appear as an interesting material for a variety of mechanical, piezoelectric, optical, and electrical applications. ZnO nanostructures used in study were grown by the lower temperature aqueous chemical growth (ACG) on a variety of substrates.

The main objective of this research studies is to investigate the piezoelectric, mechanical and electrical phenomenon of ZnO nanostructured based nanodevices on cheap, disposable and flexible substrate like paper, plastic. As low cost fabrication of nanodevices is very crucial and best choice for the upcoming years. We have successfully demonstrated that paper substrates can be used for the growth of ZnO nanostructures.

In the first part, piezoelectric power nanogenerators based on ZnO NRs / NWs on flexible paper substrates were demonstrated and output piezopotential was investigated using atomic force microscopy (AFM). Different p-type polymers like poly (3-hexylthiophene) P3HT, poly(3,4-ethylenedioxythiophene-Tosylate (PEDOT-Tos) were coated around the ZnO NRs / NWs in order to minimize the screening effect and increase the output piezopotential and it was found that by introducing a layer of p-type polymer we get more piezopotential compared to non-coated ZnO NRs / NWs. We also demonstrated the direct and converse piezoelectric response from ZnO NWs grown on lighter, flexible paper substrate for the first time by using nanoindentation technique.

In the second part, the mechanical properties like elastic modulus and hardness of ZnO NRs / NWs and NTs were investigated by using nanoindenter. Elastic modulus of a single ZnO horizontal NR was demonstrated by nanoindentation technique based on three point bending configuration.  Buckling phenomena of ZnO NRs and NTs was investigated by nanoindenter and various parameters like buckling energy, elastic modulus, critical stress, and critical strain calculated under different end conditions.

In the third part of thesis fabrication of Au/n-ZnO Schottky devices were fabricated and their electrical and optical properties were investigated by current voltage (I-V), electroluminescence (EL) and impedance spectroscopy. We investigated interface trap states of Au/n-ZnO nanorods interface by temperature dependence I-V parameters. That study reveals that the ideality factor decreases, while the barrier height increases with increase of temperature. Detailed and systematic analysis of the frequency-dependent capacitance and conductance measurements were performed to extract the information about the interface trap states. The energy of the interface states with respect to the valence band at the ZnO NR surface was also calculated. It was found that recombination-generation in the interface states are responsible for capacitance and conductance.

The effect of the post-growth annealing of Au/n-ZnO NWs Schottky diodes were examined and it was shown that light from the LEDs can be tuned from cold white light to warm white light by post growth annealing in different ambient.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 138 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1599
Nanotechnology, Zinc oxide, nanowires/ nanorods / nanotubes, piezoelectric effect, nanogenerator, flexible substrate, p-type polymers, elastic modulus, LEDs, electrical characteristics
National Category
Natural Sciences
urn:nbn:se:liu:diva-106207 (URN)978-91-7519-316-8 (print) (ISBN)
Public defence
2014-05-27, K3, Kåkenhus, Campus Norrköping, Linköpings universitet, Norrköping, 10:15 (English)
Available from: 2014-04-28 Created: 2014-04-28 Last updated: 2014-04-28Bibliographically approved

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