Strontium doping effect on characteristics of ultrasonically sprayed zinc oxide thin films
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Strontium doping effect on characteristics of ultrasonically sprayed zinc oxide thin films W. Battal1 · M. Rouchdi1 · H. Shaili1 · M. Ouafi2 · R. Essajai1 · A. Belafhaili3 · N. Hassanain1 · A. Mzerd1 Received: 9 December 2019 / Accepted: 5 June 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In the present work, Sr-doped ZnO (SZO) thin films were grown on heated glass substrates (250 °C) by the ultrasonic spray technique. The effect of strontium concentration on the structural and physical characteristics was studied. The molar ratio of strontium in the ultrasonically sprayed solution was varied from 0 to 5 at.%. Several characterization techniques have been investigated to analyze the SZO thin films. The X-ray diffraction results showed that the SZO thin films exhibited the hexagonal wurtzite structure of ZnO with a preferential orientation along (002) plane. Scanning electron microscope indicated that the surface morphology of the SZO thin films changed with the increase in Sr concentration. No impurity was present in all the SZO films which was confirmed by the elemental composition analysis. Moreover, Fourier transform infrared spectroscopy showed the chemical bonding of zinc oxide (ZnO) and confirmed the incorporation of the dopant into the ZnO lattice. From the UV–Vis studies, it was found that the optical band gap decreased from 3.34 to 3.04 eV by increasing Sr doping concentration. Measurements of the Hall Effect indicated that all the elaborated samples exhibited n type conductivity. From all the films studied, SZO (1 at.%) was the most suitable for applications in optoelectronic devices, where a large figure of merit was required. Keywords ZnO · SZO · Thin films · Ultrasonic spray · Band gap · Resistivity
1 Introduction In the recent years, transparent conductive oxides (TCO) have attracted much attention due to the compromise between the optical and electrical properties of these materials. Zinc oxide is a promising TCO because it has the distinction of being nontoxic, inexpensive [1] and its excellent properties such as a wide band gap with a direct band gap of 3.37 eV, large exciton binding energy of 60 meV [2], transparency in the visible region, low resistivity, great electrochemical stability [3] and its abundance in nature [4]. As * M. Rouchdi [email protected] 1
Centre de Recherche en Énergie, Équipe des semi‑conducteurs et technologie des capteurs pour l’environnement (STCE), Faculty of Sciences, Mohammed V University, B.P. 1014, Rabat, Morocco
2
LCS, Faculty of Sciences, Mohammed V University, B.P. 1014, Rabat, Morocco
3
Center for Electron Microscopy, Faculty of Sciences, Mohammed V University, B.P. 1014, Rabat, Morocco
a result, ZnO thin films play an important role in several fields such as gas sensors [5], solar cells [6], transistors [7] and photocatalysis [8]. Several methods have been developed to synthesis ZnO such as sol–gel [9], radiofrequency magnetron sputtering [10], hydrothermal electrochemical deposition [11], pulsed laser depositio
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