Experimental Investigation of Spray-Deposited Fe-Doped ZnO Nanoparticle Thin Films: Structural, Microstructural, and Optical Properties C. S. Prajapati, Ajay Kushwaha, and P. P. Sahay (Submitted May 4, 2013; in revised form July 22, 2013) Structural, microstructural, and optical properties of the undoped and Fe-doped zinc oxide (ZnO) thin films grown by spray pyrolysis technique using zinc nitrate as a host precursor have been reported here. X-ray diffraction spectra confirm that all the films have stable wurtzite structure and the effects of Fe dopants on the diffraction patterns have been found to be in agreement with the VegardÕs law. Scanning electron microscopy results show good uniformity and dense surface having spherical-shaped grains. Energy dispersive x-ray analyses with elemental mapping of the Fe-doped films show that the Fe dopants are incorporated homogeneously into the ZnO film matrix. The x-ray photoelectron spectroscopy spectra confirm the presence of 3+ oxidation state of Fe in the doped films. Atomic force microscopy analyses clearly show that the average surface roughness and the grain size decrease with the addition of Fe dopants. Optical studies reveal that the optical band gap value decreases on Fe doping. The 1 at.% Fe- doped film shows normal dispersion for the wavelength range 450-700 nm. The PL spectra of the films show a strong ultraviolet emission centered at ~388 nm in the case of 1 at.% Fe-doped film. A slow photo current response in the films has been observed in the transient photoconductivity measurement. Keywords Fe-doping, optical properties, surface morphol- ogy, ZnO nanoparticle thin films 1. Introduction Zinc oxide (ZnO), a wide band gap (3.36 eV at 300 K) compound semiconductor, has a stable wurtzite structure and high exciton binding energy of 60 meV (Ref 1). It has drawn the attention of many researchers because of its unique properties such as high thermal stability, non-tox- icity in nature, high transparency in visible region, good phosphor material, etc. Because of its multifunctional properties (semiconducting, magnetic, piezoelectric, etc.), this material has got wide applications in various elec- tronic and optoelectronic devices such as in transparent electrodes, solar cell windows, thin film transistor, chem- ical sensors, etc. (Ref 2-6). ZnO has been exploited in various forms such as single crystal, sintered pellets, thick films, thin films, and hetero-junctions (Ref 7-11). How- ever, thin films are more suitable for the chemical gas sensors because the gas sensing properties are related to the material surface, where the gases are adsorbed and the chemical reactions occur. More recently, this material has received a growing attention as a nanostructured material because of its excellent properties arising out of large sur- face-to-volume ratio, quantum confinement effect, etc. (Ref 12-15). As grown ZnO is an n-type semiconductor and its n- type conductivity can be controlled by doping. Various dopants like Al, In, Cu, Sn, etc., have been used to modify the microstructure and defect chemistry of the ZnO matrix. When the doped 3d transition metal (TM) ions have a valence state of 2+, equal to that of Zn, the difference be- tween the ionic radii of Zn and the 3d ions is minimized and thus the defect formation for holding the charge neutrality is suppressed. This has motivated us to investigate the influ- ence of Fe (3d TM) ions on the structural, microstructural, and optical properties of ZnO nanoparticle thin films. In the present study we have investigated the compositional homogeneity of the Fe-doped ZnO films. Energy dispersive x-ray (EDX) analyses in the scanning electron microscopy (SEM) as well as energy dispersive x-ray spectroscopy map- ping have been used to assess the low scale composition and local distribution of elements in the prepared films. In most of the research work on structural and optical properties of the Fe-doped ZnO thin films, zinc acetate has been used as a host precursor in the film preparation (Ref 16-18). However, very few reports are available on the structural and optical properties of the spray-depos- ited Fe-doped ZnO thin films using zinc nitrate as a host precursor. So in the present investigation, we have used zinc nitrate as a host precursor in the film preparation. C.S. Prajapati and P.P. Sahay, Department of Physics, Motilal Nehru National Institute of Technology, Allahabad 211004, India; and Ajay Kushwaha, Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India. Contact e-mail: dr_ppsahay@rediffmail.com. JTTEE5 22:1230–1241 DOI: 10.1007/s11666-013-9973-0 1059-9630/$19.00 Ó ASM International 1230—Volume 22(7) October 2013 Journal of Thermal Spray Technology Peer Reviewed