International Journal of Scientific and Research Publications, Volume 5, Issue 7, July 2015 1 ISSN 2250-3153 www.ijsrp.org Preparation and Characterization of Sprayed Mo-doped ZnO Films T. Sreenivasulu Reddy * , M. Vasudeva Reddy ** , K.T. Ramakrishna Reddy * * Department of Physics, Sri Venkateswara University, Tirupati, India. ** School of Chemical Engineering, Yeungnam University, Gyeongsan712-749, Republic of Korea. Abstract- Zinc oxide (ZnO) thin films doped with molybdenum (Mo) have been grown on corning 7059 glass substrates by spray pyrolysis technique. The layers were deposited for different solution concentrations ranging from 0.01M to 0.2M, keeping Mo – doping constant as 2 at. %. The change in properties of the films by varying Zn molarity was studied. X-ray diffraction studies showed polycrystalline nature of the films with (002) preferred orientation and exhibited wurtzite structure. The layers formed at 0.1M molar concentration exhibited better crystallinity compared to other layers. Raman studies are in good agreement with XRD. Surface morphology varied significantly with Zn- molar concentration. An average transmittance of the layers was 80% in the visible region and the band gap varied from 3.31 eV to 3.5 eV. The detailed analysis of the results including photoluminescence are reported and discussed. Index Terms- Thin films; ZnO: Mo; spray pyrolysis; structural properties; optical properties. I. INTRODUCTION ransparent conducting oxide films have been widely studied in recent years. ZnO is the most preferable material over other oxide thin films. Its main advantages are low cost of precursor materials, relatively low deposition temperature, non- toxicity, stability in hydrogen plasma atmosphere [1-3]. Moreover, zinc oxide thin films have been used for various applications, such as solar energy conversion [4, 5], gas sensors [6-7] and light emitting devices [8]. ZnO is an n-type semiconductor with a wide band gap. This can be doped with a wide variety of elements to meet the requirements of the field of application. Preparation of ZnO thin films with dopants like Mg, Al, B, Ga, In, Sn, F, [8-15] by using chemical spray technique was reported by many investigators. In many of these investigations, the authors reported their work using zinc acetate dihydrate (Zn (CH 3 OOH) 2 .2H 2 O) as the precursor for zinc. But, in the present work we used zinc chloride (ZnCl 2 ) as the precursor with Mo-dopant [16]. Molybdenum is the potential dopant material for improving conductivity and transparency of zinc oxide thin films. Mo-doping in ZnO lattice is very beneficial because of a valence difference of 4 between Mo 6+ and Zn 2+ , thus enabling each dopant atom of dopant to contribute 4 free electrons to the electrical conductivity. Mo-dopant appears to be very successful because of its smaller ionic radius 0.06nm [17]. Mo-doped ZnO films have been grown using different methods such as RF and DC sputtering [18-19] and the ion beam sputtering deposition [20]. In comparison of the films grown by spray pyrolysis, it is quite simple and the required experimental set-up is less expensive and flexible for process modification. Furthermore to produce large area films, spray pyrolysis is easily adoptable. There are less investigations on Mo-doped ZnO films by spray pyrolysis method in literature. In this work we report on the growth of Mo-doped ZnO (MZO) films by chemical spray process and the results on film characterization. II. EXPERIMENTAL Mo-doped ZnO thin layers were prepared by the spray pyrolysis method on corning 7059 glass substrates at a constant substrate temperature of 400 o C. Zinc chloride (ZnCl 2 , Aldrich 98%) and molybdenum chloride (MoCl 5 , Aldrich 95%) were used as precursors for of zinc and molybdenum respectively. Methanol was used as solvent for preparation of precursor solutions. The Zn molarity was varied in the range 0.01M - 0.2M, to investigate its effect on the preparation of MZO thin films. The solution was sprayed at a flow rate of 6ml/min and compressed air was used as the carrier gas with a flow rate of 8l/min. A distance of 25cm was maintained between substrate and the nozzle. The solution was sprayed for 15s and paused for 1min to overcome cooling of the substrates. The deposition was carried out using automated stepper motor system to get uniform coating of the film on the substrate. The structural properties were studied using a Siefert X-Ray diffractometer (XRD) with a CuK α radiation source (λ=1.542 Å). Raman studies were carried out using Horiba Lab Ram HR spectrometer using a laser of wavelength 532nm for excitation. FSI serion scanning electron microscope was used for surface morphology studies. The optical properties were determined using UV-Vis-NIR spectrophotometer (Perkin Elmer lamda –950). The photoluminescence properties of the films was studied by YVON Florolog-3 (model:FL3-22) with xenon flash lamp as source. III. RESULTS AND DISCUSSIONS The as-grown MZO films were uniform, pin hole free, pale whitish in appearance and strongly adherent to the substrate surface. The film surface was found to be rough. The X-ray diffraction spectra of MZO films formed using different Zn- concentrations with 2 at. % Mo-doping are shown in fig 1. All the films were polycrystalline in nature and showing a structure with the appearance of (100), (002) and (101) peaks. The crystal structure of the grown films was evaluated to be hexagonal wurtzite. With the increase of solution molarity, the intensity of the (002) peak increased up to the molarity of 0.1M and afterwards it is decreased. When the Zn concentration in the solution was higher than 0.1M, the (102), (103) and (112) T