Effect of deposition rate on the structural, optical and electrical properties of Zinc oxide (ZnO) thin films prepared by spray pyrolysis technique
Introduction
Zinc oxide (ZnO), an II – IV semiconductor, has a wide direct gap of 3.37 eV at room temperature and large exciton binding energy of 60 meV [1], [2], [3], which has attracted much attention for its wide prospects optoelectronic devices such as solar cells, light emitting diodes (LED), laser diodes and acoustic – optical devices [4], [5], [6], [7], [8]. In solar cells, ZnO thin films are used as an anti-reflective coating (ARC) and transparent conductive oxide (TCO) due to its high optical transmittance in the visible light region, high band gap energy (e.g., ∼3.3 eV), optimum refractive index (n ∼ 2.0) and natural n-type electrical conductivity [9], [10], [11]. ZnO can be used as a heat mirrors, piezoelectric devices [12], thin films [13] and chemical and gas sensing [14].
ZnO thin films have been prepared using various methods such as molecular beam epitaxy (MBE) [15], chemical vapor deposition [16], electrochemical deposition [17], pulsed laser deposition (PLD) [18], sol-gel process [19], reactive evaporation [20], magnetron sputtering technique [21] and spray pyrolysis [22], have been reported to prepare thin films of ZnO. The spray pyrolysis technique is one of these techniques to prepare large-scale production for technological applications. It is possible to alter the mechanical, electrical, optical and magnetic properties of ZnO nanostructures.
Many researchers have studied the effects of microstructure and processing on electrical conduction in ZnO nanostructures [23], [24], [25], [26]. It is known that ZnO films prepared by the spray pyrolysis technique can have a wide band gap between 3 and 3.37 eV, El Sayed et al. [27] had controlled the effect of cadmium content on the film structure and optical absorption for this ZnO microstructured.
In present study, nanostructure ZnO based thin films can be deposited by spray pyrolysis technique on glass substrate where substrate temperatures are maintained at 350 °C for all experimentation. The thin films were deposited at different rates, the aim of this work to study the effect of deposition rate on crystalline structure, optical gap energy and electrical conductivity.
Section snippets
Experimental
ZnO solution were prepared by dissolving 0.1 M (Zn(CH3COO)2, 2H2O) in the solvent containing equal volume absolute methanol solution (99.995%) purity, then we have added a few drops of concentrated HCl solution as a stabilizer, the mixture solution was stirred at 60 °C for 120 min to yield a clear and transparent solution. The substrate was R217102 glass in a size of 30 cm × 7.5 cm × 0.1 cm, prior to pumping, the substrate (R217102 glass) were cleaned with alcohol in an ultrasonic bath and blow-dried
The crystalline structure of ZnO thin films
The X-ray diffraction (XRD) spectrum of the ZnO thin films is shown in Fig. 1. The obtained XRD spectra matched well with the space group P63mc (186) (No. 36-1451) [28]. As it can be seen the only diffraction peak was observed at 2θ 34.5°, which is related to the plan of (0 0 2). The peak at position 34.5° corresponding to the (0 0 2) plans is very sharp, the film obtained with 30 ml has higher and sharper diffraction peak indicating an improvement in (0 0 2) peak intensity compared to other films,
Conclusions
In conclusion, highly transparent conductive ZnO thin films were deposited on glass substrate by spray pyrolysis technique. The ZnO thin films were deposited at 350 °C, the substrates were heated by using the solar cells method. The substrate was R217102 glass in a size of 30 cm × 7.5 cm × 0.1 cm. The influence of deposition rate on structural, optical and electrical properties was investigated. Nanocrystalline films with a hexagonal wurtzite structure with a strong (002) preferred orientation were
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