Effect of Fe incorporation on the optical behavior of ZnO thin films prepared by sol-gel derived spin coating techniques R. Ajay Rakkesh, R. Malathi, and S. Balakumar Citation: AIP Conf. Proc. 1512, 1200 (2013); doi: 10.1063/1.4791480 View online: http://dx.doi.org/10.1063/1.4791480 View Table of Contents: http://proceedings.aip.org/dbt/dbt.jsp?KEY=APCPCS&Volume=1512&Issue=1 Published by the AIP Publishing LLC.
Additional information on AIP Conf. Proc. Journal Homepage: http://proceedings.aip.org/ Journal Information: http://proceedings.aip.org/about/about_the_proceedings Top downloads: http://proceedings.aip.org/dbt/most_downloaded.jsp?KEY=APCPCS Information for Authors: http://proceedings.aip.org/authors/information_for_authors
Downloaded 12 Oct 2013 to 14.139.186.162. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://proceedings.aip.org/about/rights_permissions
Effect of Fe Incorporation on the Optical Behavior of ZnO Thin Films Prepared By Sol-Gel Derived Spin Coating Techniques R. Ajay Rakkesh, R. Malathi and S. Balakumar# National Centre for Nanoscience and Nanotechnology, University of Madras, Guindy Campus, Chennai, India # email:
[email protected]
Abstract. In this work, Fe doped Zinc Oxide (ZnO) thin films were fabricated on the glass substrate by sol-gel derived spin coating technique. X-ray Diffraction studies revealed that the obtained pure and Fe doped ZnO thin films were in the wurtzite and spinel phase respectively. The three well defined Raman lines at 432, 543 and 1091 cm-1 also confirmed the lattice structure of the ZnO thin film has wurtzite symmetry. While doping Fe atoms in the ZnO, there was a significant change in the phase from wurtzite to spinel structure; owing to Fe (III) ions being incorporated into the lattice through substitution of Zn (II) ions. Room temperature PL spectra showed that the role of defect mediated red emissions at 612 nm was due to radial recombination of a photogenerated hole with an electron that belongs to the Fe atoms, which were discussed in detail. Keywords: ZnO, Fe, Nanostructures, Thin film. PACS: 78.66.-w
INTRODUCTION RESULTS AND DISCUSSIONS
In recent years, transition metal (TE) doped ZnO semiconducting nanomaterials have been widely investigated because of their ferromagnetic and magnetic transport properties as diluted magnetic semiconductor and in cancer therapy[1-2]. A few reports covering the optical properties of Fe doped ZnO nanostructures have appeared [3-4]. In this paper, we have reported the fabrication of Fe-doped ZnO thin films by sol-gel derived spin coating techniques and their structural, morphological aspects and optical behaviours.
The diffraction peaks of annealed pure ZnO thin films were correspond to wurtzite structure without any other impurities as shown in Fig 1(inset). The appearance of two additional diffraction peaks of (3 1 1) and (3 3 3) in addition to ZnO peaks indicated the spinel phase due to incorporation of Fe (III) ions in the ZnO lattices where the ionic radius of Fe3+ (0.064nm) is smaller than Zn2+ (0.074nm) ions (JCPDS. 221012). The intensity of the ZnO main peak (002) decreased with increase of Fe concentration. The morphology of the thin films were imaged by FESEM and found that the nanosphered particles of pure ZnO with average diameter of ~20nm were shown in Fig 2(a).
PREPARATION DETAILS Thin films of ZnO (Fe) were prepared by dissolving 4.32g of Zinc Acetate and 3.78g of oxalic acid in 50ml of double distilled water. After stirring for an hour, 0.5M% of Iron acetate was added to the prepared solution. The sols were stirred until we obtain a clear solution. The obtained sol was dropped onto the substrate fixed on the spin coater and then spun at 2400 rpm for 60 seconds. Further, these films were then annealed at 400°C for 2 h to crystallize the deposited films.
SOLID STATE PHYSICS: Proceedings of the 57th DAE Solid State Physics Symposium 2012 AIP Conf. Proc. 1512, 1200-1201 (2013); doi: 10.1063/1.4791480 © 2013 American Institute of Physics 978-0-7354-1133-3/$30.00
1200 Downloaded 12 Oct 2013 to 14.139.186.162. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://proceedings.aip.org/about/rights_permissions
FIGURE 1. XRD Pattern of pure and different concentration of Fe doped ZnO thin films
The photoluminescence spectrum of Fe doped ZnO thin films are shown in Fig 4. The narrow UV band at ~ 385 nm can be explained by near edge transition of wide band gap of pure ZnO [5]. On incorporating 5 to 15% of Fe atoms on the Zn site, the shift in the UV band towards the lower side and peak appeared at 373 nm and the defect mediated red emission observed at 612 nm. Upon increase to 20%, the UV band shifted further down to 366 nm and a red band emission at 612 nm with higher intensity. It is evident that the formation of defect related red emissions owing to radial recombination of a photogenerated hole with an electron that belongs to the Fe (III) atoms.
FIGURE 2. FESEM micrographs of Fe doped ZnO thin films with varying Fe concentrations
While incorporation 5% of Fe in ZnO, it showed the formation of particles with nanospikes morphology of average width ~18-24nm (Fig 2b). Upon increasing the Fe doping to 10, 15 and 20% in ZnO, it resulted in nanoclusters (Fig 2c) of average diameter ~15-20nm, nanofibres (Fig 2d) with ~20-40nm width and the combination of nanofibres and nanospikes (Fig 2e) with ~15-50nm width respectively. It was found that, when Fe atoms were doped with ZnO nanoparticles, there was a morphological evolution from nanospheres to nanofibres. The incorporation of Fe inhibited the rate of particle growth, whereas it also promoted the rate of nucleation, thus end up producing more number of nanoparticles with different morphologies.
FIGURE 4. PL spectra of pure and different concentrations of Fe doped ZnO thin films
CONCLUSIONS In summary, Fe doped ZnO thin films were fabricated successfully by sol-gel derived spin coating technique. The thin films were crystalline in nature with wurtzite and spinel phase of pure and Fe doped ZnO respectively. The PL spectra at room temperature showed strong and narrow red emission at 612 nm. The red emissions were attributed to the radial recombination of a photogenerated hole with an electron that belongs to Fe atoms. We believe that these thin films could be used to fabricate lightemitting device in optoelectronic applications.
Laser Raman studies were carried out with laser light of wavelength 532nm. Raman spectrum has the peaks at 432, 543 and 1091 cm-1; confirmed that the wurtzite structure of ZnO was retained. While Fe (III) ions were being incorporated into the lattice through substitution of Zn (II) ions, the wurtzite was transformed to spinel phase.
ACKNOWLEDGMENTS R. Ajay Rakkesh acknowledges University of Madras for providing NCNSNT fellowship (C2/AL/2011/388) to carry out his research work.
REFERENCES 1. 2. 3. FIGURE 3. Laser Raman spectra of Fe doped ZnO thin films
4. 5.
T. Liu, H. R. Xu, W. S.Chin, P.Yang, Z. H Yong, A. T. S.Wee, J. Phys.Chem. C. 112 (2008) 13410–3418. K. C. Barick, M. Aslam, V. P. Dravid, D. Bahadur, J. Phys. Chem. C 112 (2008), 15163–15170. S. H. Baek, J. J. Song, S. W. Lim, Physica B 399 (2007), 101–104. V. Gupta, P. Blattacharya, Y. I. Yusuk, K. Sreenivas, R. S. Katiyar, J. Cryst. Growth. 287 (2006), 39–43. Y. C. Kong, D. P. Yu, B .Zhang, W. Fang S.Q. Feng, Appl. Phys. Lett. 78 (2001) 407.
1201 Downloaded 12 Oct 2013 to 14.139.186.162. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://proceedings.aip.org/about/rights_permissions
