Structural, optical and electrical properties of cobalt doped zinc oxide thin films prepared by spray pyrolysis

Abstract

Diluted magnetic semiconductors (DMSs) have been extensively studied due to their great importance in spintronics devices. Among the family of DMSs, wide bandgap Zinc oxide (ZnO)-based DMS is rather significant as their potential in practical applications in opto-electronic device. Cobalt (Co) doped ZnO films were synthesized from the precursors Zn(CH3COO)2.2H2O and Co(CH3COO)2.4H2O by using a “Spray Pyrolysis Deposition” technique at 573 K substrate temperature containing 0.00, 0.05, 0.15, 0.25 and 0.35% Co concentrations. The surface morphological, structural, electrical and optical properties of the as-deposited ZnO films have been investigated as a function of Co-doping level. The thickness of the films was estimated by Fizeau fringes interference method which varied from 190 to 210 nm. The scanning electron microscopy (SEM) micrographs of as-deposited films show uniform surface and deposition covers the substrate well. Nanofibers are observed around the nucleation centre of as-deposited thin films. Energy Dispersive Analysis of X-ray (EDAX) results clearly showed that the grains are typically comprised of both Zn and O for pure and Zn, O and Co for Co doped films. From EDAX (EDX) data it is found that atomic weight % of Co is increased with the increase of Co concentration in Co doped ZnO films. X-ray diffraction studies showed the amorphous polycrystalline nature of the films with preferential orientation along the (100), (002), (101), (102), and (110) planes. Structure of the material has been identified as hexagonal wurtzite. The peaks are found to shift from their standard positions in the presence of the Co dopant. There is a deviation in the lattice parameters and it may be happened due to the positioning of dopant atoms into the interstitial lattice sites. Various optical constants such as absorbance, transmittance, refractive index and dielectric constant of the films have been studied for the as-deposited films are recorded in the wavelength ranges from 300 to 1100 nm. For as-deposited Zn1-xCoxO films, the band gap varies from 3.2 to 2.7 eV as Co increases. The optical transmittance of the films is found to decrease from 80 % to 70 % (at initial) with the addition of Co doping. Activation energy of Zn1-xCoxO films is found to decreases with the incorporation of Co in the solution.