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Defect Driven Emission from ZnO Nano Rods Synthesized by Fast Microwave Irradiation Method for Optoelectronic Applications

Published online by Cambridge University Press:  28 February 2014

Nagendra Pratap Singh ,
S.A. Shivashankar  and
Rudra Pratap
Nagendra Pratap Singh
Affiliation:
Department of Mechanical Engineering, Indian Institute of Science, Bangalore-560012, India Centre for Nano Science and Engineering (CeNSE), Indian Institute of Science, Bangalore-560012, India
S.A. Shivashankar
Affiliation:
Centre for Nano Science and Engineering (CeNSE), Indian Institute of Science, Bangalore-560012, India
Rudra Pratap
Affiliation:
Department of Mechanical Engineering, Indian Institute of Science, Bangalore-560012, India Centre for Nano Science and Engineering (CeNSE), Indian Institute of Science, Bangalore-560012, India
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Abstract

Because of its large direct band gap of 3.37 eV and high exciton binding energy (∼60 meV), which can lead to efficient excitonic emission at room temperature and above, ZnO nanostructures in the würtzite polymorph are an ideal choice for electronic and optoelectronic applications. Some of the important parameters in this regard are free carrier concentration, doping compensation, minority carrier lifetime, and luminescence efficiency, which are directly or indirectly related to the defects that, in turn, depend on the method of synthesis. We report the synthesis of undoped ZnO nanorods through microwave irradiation of an aqueous solution of zinc acetate dehydrate [Zn(CH3COO)2. 2H2O] and KOH, with zinc acetate dihydrate acting as both the precursor to ZnO and as a self-capping agent. Upon exposure of the solution to microwaves in a domestic oven, ZnO nanorods 1.5 µm -3 µm and 80 nm in diameter are formed in minutes. The ZnO structures have been characterised in detail by X-ray diffraction (XRD), selective area electron diffraction (SAED) and high-resolution scanning and transmission microscopy, which reveal that each nanorod is single-crystalline. Optical characteristics of the nanorods were investigated through photoluminescence (PL) and cathodoluminescence (CL). These measurements reveal that defect state-induced emission is prominent, with a broad greenish yellow emission. CL measurements made on a number of individual nanorods at different accelerating voltages for the electrons show CL intensity increases with increasing accelerating voltage. A red shift is observed in the CL spectra as the accelerating voltage is raised, implying that emission due to oxygen vacancies dominates under these conditions and that interstitial sites can be controlled with the accelerating voltage of the electron beam. Time-resolved fluorescence (TRFL) measurements yield a life time (τ) of 9.9 picoseconds, indicating that ZnO nanorods synthesized by the present process are excellent candidates for optoelectronic devices.

Keywords

defectsluminescencenanostructure
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1633: Symposium R – Oxide Semiconductors , 2014 , pp. 75 - 80
Copyright
Copyright © Materials Research Society 2014 

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References

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