The effect of Al-doping on the structural, optical, electrical and cathodoluminescence properties of ZnO thin films prepared by spray pyrolysis

https://doi.org/10.1016/j.physb.2010.02.025Get rights and content

Abstract

Aluminum doped zinc oxide (Al-doped ZnO) thin films were deposited by the spray pyrolysis technique onto the glass substrates at 450 °C using anhydrous zinc chloride (ZnCl2) and aluminum chloride (AlCl3) as sources of zinc and aluminum ions, respectively. The effect of [Al]/[Zn] ratio in the solution on the structural, optical, electrical and cathodoluminescence properties of these films were investigated. XRD study revealed that both undoped and Al-doped ZnO films were polycrystalline with hexagonal structure and exhibited (0 0 2) preferential orientation. The optical and electrical studies showed that the film deposited with the [Al]/[Zn] ratio equal to 0.05 had high transmittance (of about 80% and 95% in the visible and near infra-red regions, respectively) and minimum resistivity of 1.4×10−3 Ω cm, respectively. This resistivity value decreased with increase in temperature indicating the semiconducting nature of Al-doped ZnO films. The chemical composition analysis (EPMA) showed that this film was nearly stochiometric with a slight oxygen deficiency.

Introduction

Transparent conducting ZnO thin films have recently gained much attention due to the many advantages over other oxide thin films like ITO, CdO, SnO2, etc. These advantages include nontoxicity, low cost, high electrical conductivity and transparency. ZnO can be doped with a wide variety of ions. Typical doping that has been used to produce conducting ZnO films was Al [1], In [2], Ga [3], Sn [4], N [5], etc. The films of ZnO can be used as gas sensors [6], transparent electrodes in optoelectronic and solar cells devices [7], [8], laser diodes [9] and light emitting diodes [3]. There are several deposition techniques that have been employed to grow undoped and doped ZnO thin films like chemical vapor deposition (CVD) [10], magnetron sputtering [11], pulsed laser deposition (PLD) [12], sol–gel process [13] and spray pyrolysis (SP) [14], [15]. This latter method is used successfully in our laboratory to elaborate a variety of materials such as In2O3 [16], WO3 [17], Fe2O3 [18], ZnS [19], CeO2 [20], etc. Furthermore, this technique is quite simple and the required set-up is less expansive and flexible for process modifications. Additionally, by using this technique one can produce large area films without the need of a high vacuum and the produced films can be controlled step by step. In this work, undoped and Al-doped zinc oxide thin films are prepared by spray pyrolysis. The effect of [Al]/[Zn] ratio on the structural, optical, electrical and cathodoluminescence properties of these films is studied.

Section snippets

Experimental procedure

Zinc oxide films were prepared from solution of zinc chloride ZnCl2 dissolved in deionized water and transported in tubes using a pump flowmeter to regulate the spray rate of the solution, which is sprayed on fine droplets using air as carrier gas. The aluminum chloride (AlCl3) was used as source of Al3+ ions (dopant) with the [Al]/[Zn] ratio varied between 0 and 0.10. This solution was sprayed onto clean glass substrates (glass microscope slide) heated by a ceramic heater. The zinc chloride

Crystal structure determination

The X-ray diffraction patterns of Al-doped ZnO thin films deposited with different [Al/[Zn] ratios (0, 0.02, 0.05, 0.07 and 0.10) are shown in Fig. 2 (a–e). The interplanar spacing values dhkl corresponding to the (1 0 0), (0 0 2), (1 0 1), (1 0 2) and (1 0 3) diffraction planes are compared with the standard values [22]. A matching of the calculated dhkl values and the standard ones confirms that all the deposited films (undoped and Al-doped ZnO) are crystallized in the hexagonal structure with a

Conclusion

After conducting, transparent undoped and Al-doped ZnO thin films were deposited by the spray pyrolysis technique under optimum conditions (zinc chloride concentration of 0.05 M, solution flow rate of 5 ml/min and substrate temperature at 450 °C). The influence of Al doping on the structural, optical, electrical and cathodoluminescence properties of ZnO films is presented. Undoped and Al-doped ZnO films are found to be polycrystalline with hexagonal wurtzite structure strongly oriented along the (0

References (31)

  • H. Zhou et al.

    Thin Solid Films

    (2007)
  • C. Tsay et al.

    Thin Solid Films

    (2008)
  • J. Zhao et al.

    J. Cryst. Growth

    (2005)
  • T. Pauporté et al.

    Electrochim. Acta

    (2000)
  • D. Gal et al.

    Thin Solid Films

    (2000)
  • K. Haga et al.

    Thin Sold Films

    (1999)
  • T. Minami et al.

    Thin Solid Films

    (2000)
  • M. Regragui et al.

    Thin Solid Films

    (2000)
  • L. Dghoughi et al.

    Appl. Surf. Sci.

    (2006)
  • B. Elidrissi et al.

    Thin Solid Films

    (2000)
  • A. Dakhel

    Sol. Energy

    (2008)
  • J.S. Kim et al.

    Thin Solid Films

    (1992)
  • J.F. Chang et al.

    J. Cryst. Growth

    (2000)
  • P. Nunes et al.

    Vacuum

    (1999)
  • T. Minami et al.

    J. Lumin.

    (1981)
  • Cited by (56)

    • Red-orange photoluminescence emission of sol-gel dip-coated prepared ZnO and ZnO:Al nano-crystalline films

      2019, Journal of Luminescence
      Citation Excerpt :

      Indeed, Al showed promising additive in zinc oxide for improving optoelectronic characteristics of devices, these properties also are depended strongly on the technique applied to produce ZnO films. There are various techniques including sol-gel, spin coating sol-gel, spray pyrolysis, laser pulse, magnetron sputtering and metalorganic chemical vapor deposition (MOCVD) [7,17,18,23,26–29]. The sol-gel technique based on hydrolysis of precursors is of great interest [30,31], due to have the advantage of being simple and low-cost process.

    • Influence of yttrium doping on the structural, morphological and optical properties of nanostructured ZnO thin films grown by spray pyrolysis

      2019, Ceramics International
      Citation Excerpt :

      Another question that could contribute to this difference could be the eventual anisotropy in particle shape, since measurements in the SEM images are performed in a direction parallel to the film surface and XRD provides a size which takes into account different directions. These differences have been also found in Al-doped ZnO films prepared by spray pyrolysis [48]. On the other hand, the chemical composition of ZnO:Y films was confirmed by energy dispersive X-ray spectroscopy (XEDS).

    • Synthesis and characterization of ZnO:Ni thin films grown by spray-deposition

      2017, Ceramics International
      Citation Excerpt :

      At present, a number of ZnO films doped with various metallic ions have been widely studied for the manipulation of their optical and electrical properties. It was found that the doping of ZnO with some metallic ions such as indium, aluminum, magnesium, nickel, and boron improves its structural, optical, and electrical properties [6–12]. Ni2+ has a standard ionic radius of 0.069 nm, which is slightly less than that of Zn2+ (0.074 nm), and this information permits predicting that Ni2+ ions can substitute Zn2+ ions in the crystalline structure of ZnO [13].

    • Influence of laser doping on nanocrystalline ZnO thin films gas sensors

      2017, Progress in Natural Science: Materials International
    View all citing articles on Scopus
    View full text