Elsevier

Physica B: Condensed Matter

Volume 523, 15 October 2017, Pages 31-38
Physica B: Condensed Matter

Structural, optical and nonlinear optical studies of AZO thin film prepared by SILAR method for electro-optic applications

https://doi.org/10.1016/j.physb.2017.08.021Get rights and content

Abstract

Aluminium doped (i.e. 3 at%) zinc oxide (AZO) thin films were prepared by simple successive ionic layer adsorption and reaction (SILAR) method with different dipping cycles. The structural and surface morphology of AZO thin films were studied by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The optical parameters such as, transmittance, band gap, refractive index, extinction coefficient, dielectric constant and nonlinear optical properties of AZO films were investigated. XRD pattern revealed the formation of hexagonal phase ZnO and the intensity of the film was found to increase with increasing dipping cycle. The crystallite size was found to be in the range of 29–37 nm. Scanning Electron Microscope (SEM) images show the presence of small sized grains, revealing that the smoothest surface was obtained at all the films. The EDAX spectrum of AZO conforms the presence of Zn, O and Al. The optical transmittance in the visible region is high 87% and the band gap value is 3.23 eV. The optical transmittance is decreased with respect to dipping cycles. The room temperature PL studies revealed that the AZO films prepared at (30 cycles) has good film quality with lesser defect density. The third order nonlinear optical parameters were also studied using Z-scan technique to know the applications of deposited films in nonlinear devices. The third order nonlinear susceptibility value is found to be 1.69 × 10−7, 3.34 × 10−8, 1.33 × 10−7and 2.52 × 10−7 for AZO films deposited after 15, 20, 25 and 30 dipping cycles.

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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