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