Elsevier

Vacuum

Volume 141, July 2017, Pages 210-215
Vacuum

Short communication
The Al doping effect on the surface, optical, electrical and nanomechanical properties of the ZnO and AZO thin films prepared by RF sputtering technique

https://doi.org/10.1016/j.vacuum.2017.04.025Get rights and content

Highlights

  • ZNO and AZO thin films deposited by RF magnetron sputtering.

  • Crystallographic structures was analyzed.

  • Nano-hardness measurements were done.

Abstract

In this study, ZnO and aluminum doped ZnO (AZO) thin films were deposited at constant RF power of 100 W for the determine of the structural, surface, optical, electrical and nanomechanical properties. X–Ray diffraction (XRD), atomic force microscopy (AFM), nanoindentation technique and UV–Vis spectrophotometer were used. ZnO (100) and ZnO (004) orientations were detected in the ZnO and AZO films. The crystallite size values for the films were calculated as to be as 35 nm and 20 nm for ZnO and AZO thin films, respectively. It was found that the roughness values decreased to 3.15 nm from 5.15 nm for AZO and ZnO films, respectively. The hardness values of the ZnO and AZO thin films are measured as 7 GPa and 11 GPa. Young's modulus values were determined as 155 GPa and 95 GPa for ZnO and AZO films, respectively. The ZnO and AZO thin films have high transparency.

Introduction

Zinc oxide has classified in the II – VI compound semiconductor. The wide range application fields of ZnO thin films such as optoelectronics [1], sensors [2], surface acoustic wave [3], piezoelectric materials [4], the organic light emitting devices (OLED) [5], solar energy cells [6], photocatalysis [7], transparent conductive oxide (TCO) and batteries [8] encourage researchers to focus on and investigated the films characteristics in detail. ZnO thin films have the high optical transmittance, piezoelectric properties, large band gap (3.35–3.37 eV), high transparency, high exciton binding energy, high coupling factor and room temperature ferromagnetism features [9], [10], [11]. The spray pyrolysis [12], pulse laser deposition (PLD) [13], sputtering method [14], molecular beam epitaxy (MBE) [15], electron beam evaporation [16], chemical vapor deposition [17], sol – gel process [18], plasma enhanced chemical vapor deposition (PECVD) [19] techniques exerted to prepared ZnO films in the different desired size and concentrations. Beside of the known advantages of un-doped ZnO films, it is not preferred because of instability and low conductivity, especially at the high temperature. Therefore, ZnO films are used to doped with elements. In the past decades, many elements same as aluminum [20], magnesium [21], gallium [22], ytterbium [23], silver [24], titanium [25], copper [26] and etc have been investigated for doped properties and performance for various aim applications.

Due to a relatively low price, abundance, thermal stability, high refractive index and non-toxicity, AZO materials are an alternative to well-known indium tin oxide (ITO) films [[27], [28], [29], [30], [31], [32]]. Surface morphology, crystal structure, and doping level have been influencing on the mechanical properties of obtained films. For calculating of the mechanical properties of AZO films, the nanoindentation methods have been extensively used [33], [34]. The nanoindentation method is very easy operation [35]. The contact depth of the nanoindentation is limited and it must be less than 10% of the film thicknesses [36].

In this study, Al doping effects on the surface, optical, electrical and nanomechanical properties of the ZnO and AZO thin films prepared by RF sputtering technique were investigated. All films were deposited by same production parameters. Film thicknesses were determined by interferometric measurements. Microstructural properties were analyzed by XRD device. Surface and nano indentation measurements were done by atomic force microscopy (AFM). UV-Vis spectrophotometer and interferometer were used for the measure absorbance, transmittance, refractive index, extinction coefficient and band gap energy determination. Moreover, electrical properties were realized for the determine sheet resistance and resistivity measurements.

Section snippets

Experimental

Prior to a deposition, the glasses substrate were cleaned using acetone and ethyl alcohol. The cleaned glasses putting up in the chamber and evacuated to the base pressure of 2 × 10−2 Torr. The high purity argon gas (99.999%) sent into the vacuum chamber as a buffer gas. All parameters during the procedure were listed in Table 1. Thicknesses of deposited films on the substrate were checked using in-situ thickness measurement controller.

Result and discussion

The thicknesses of the films were determined as 40 nm and 300 nm by Filmetrics F20 thin film thickness measurement system in the very high Goodness of Fit (GOF) value of 0.999 for ZnO and AZO thin films, respectively. The Cauchy model was used for the determination of the thicknesses of the films.

X – Ray diffractometer (XRD) for microstructural properties of ZnO and AZO films were used in the range of 30°–80°. The XRD patterns of obtaining samples are shown in Fig. 1a and b. The ZnO and AZO

Conclusion

In this paper, Al doping effects were investigated for the In conclusion, the ZnO, and Al – doped ZnO (AZO) thin films. ZnO and AZO thin films were deposited on glass substrates by using the RF sputtering deposition technique. The structure, surface, mechanical optical and electrical properties of samples have been studied by XRD, AFM, nanoindentation and UV–Vis spectrophotometer. The XRD patterns show the polycrystalline structure for Al-doped and un-doped ZnO thin films. These results show

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