Structural, optical and nonlinear optical studies of AZO thin film prepared by SILAR method for electro-optic applications
Introduction
Nonlinear optical semiconductor materials are of the great importance, as they alter the optical properties of light propagating through them and hence used in many applications such as optoelectronic devices, all optical signal processing, optical image processing, optical switching, optical limiting, optical information storage, high speed optical communication networks, optical waveguides, and future applications in biological and medical sciences [1]. Nonlinear optical properties of the metals oxides thin films have a great attraction now a day. ZnO has promising optoelectronic applications due to its good third order nonlinear generation [2], [3]. Optical, nonlinear optical and electrical properties of ZnO can be tuned by suitable dopants. Metal doped ZnO thin films are used as a transparent conducting electrodes (TCE) in solar cell and optical waveguides [4]. When doped with aluminium, it shows low electrical resistance [5], [6] combined with high optical transmittance in the visible and near infrared range, thus being competitive with indium tin oxide for application as a transparent electrode [7]. Zinc oxide (ZnO) is II–VI compound semiconductor, having a wide band gap of 3.37 eV and high exciton binding energy of 60 meV at room temperature [8].
Aluminium doped zinc oxide (AZO) thin films can be prepared by different deposition methods. Every deposition method has its advantages and disadvantages according to their use. AZO thin films can be fabricated via chemical vapour deposition [9], pulsed laser deposition [10], spray pyrolysis [11], RF magnetron sputtering [12], sol gel [13] and SILAR method [14]. SILAR method is a one of best preparation method to produce Aluminium-doped zinc oxide (AZO) thin films. This procedure can be applied on any kind of substrate and the thickness can be easily controlled and also easy to handle. Therefore both thin and thick films can be prepared by this method.
To the best of our knowledge, in the previous reports of Al doped ZnO thin film using SILAR method, the nonlinear optical properties are not investigated. In the present study, we investigate for the first time to the nonlinear optical properties, structural and dielectric properties of AZO thin films using simple and low cost SILAR method. The nonlinear optical response of thin films are of particular interest because of its application in integrated nonlinear optical devices [15]. In this article, we present the nonlinear optical properties of the AZO films on glass substrates with different dipping cycles such as 15, 20, 25 and 30.
Section snippets
AZO film preparations at different dipping cycles
AZO thin films were prepared on glass substrates by SILAR method. In the experiments, 0.1 M zinc chloride anhydrous (ZnCl2), 3 at% of aluminium chloride hexahydrate (AlCl3·6H2O) and concentrated ammonia (NH4OH) were used to prepare the zinc complex ([Zn (NH3)4]2+) solution. Ammonia (NH4OH) was added to adjust the pH of the solution to 12. For prepared AZO films, different dipping cycles were allowed to the test on crystallinity and nanostructure thin film. The five different rinsing steps as
Structural studies
Fig. 1 shows the XRD patterns of AZO thin films on glass substrates with different dipping cycles such as 15, 20, 25 and 30. It is found that all the thin films have corresponding to (100), (002), (101) and (102) plane. However, the intensity of the (002) is much stronger than that of other planes. This indicates that the c axis of the grains becomes uniformly perpendicular to the substrate surfaceafterincreasing the dipping cycles represented the increase in intensity of the (002) plane. All
Conclusion
In this study, the structural, optical, dielectric and non-liner optical properties AZO thin films were studied at different dipping cycles by SILAR.
- (a)
The XRD result shows the films are polycrystalline nature and the crystallite size of AZO thin films are increased with dipping cycles. Morphological studies showed the highly homogeneous smooth surface of all films.
- (b)
The optical transmittance of AZO thin films exhibits high transmittance (87%) in visible region. The dielectric properties also
Acknowledgements
The authors extend their appreciation to the Deanship of Scientific Research at King Khalid University for funding this work through Research Groups Program under Grant no. R.G.P.2/3/38.
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