Synthesis and characterization of copper doped zinc oxide thin films deposited by spray pyrolysis technique

Abstract

Zinc Oxide (ZnO) is one of the most important candidates for a II-VI room-temperature diluted magnetic semiconductor (DMS) by doping with a transition metal. ZnO based DMSs are particularly attractive as candidates for integrating optical and electronic properties into a single substance. ZnO and copper (Cu) doped ZnO thin films were synthesized from the precursors Zn(CH3COO)2.2H2O and Cu(CH3COO)2.H2O by using a “Spray Pyrolysis Deposition” technique at 623K substrate temperature containing 0, 5, 9, 15, 20 and 25 at% Cu concentrations. The surface morphological, structural, electrical and optical properties of the as-deposited ZnO films have been investigated as a function of Cu-doping level. The thickness of the films was estimated by Fizeau fringes interference method which varied from 195 to 198 nm. The scanning electron microscopy (SEM) micrographs of as-deposited films shows that all the films are found well covered on the glass substrate. Nanofibers are observed around the nucleation center in pure ZnO thin film. Due to interstitial holes of ZnO are filled with copper, the fiber has broken and transform into grain. The size of the grain decreases with the increase of Cu concentration. 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 Cu for Cu doped films. From EDAX data it is found that atomic weight % of Cu is increased with the increase of Cu concentration in Cu doped ZnO films. X-ray diffraction studies showed the amorphous polycrystalline nature of the films with preferential orientation along the (100), (002), (101), (102), (110), (103) and (112) 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 Cu dopant due to the positioning of dopant atoms into 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-xCuxO films, the band gap varies from 3.21 to 3.05 eV as Cu increases. The resistivity gradually decreases with the increase of temperature, which indicates the semiconducting nature of the materials. The activation energy is increasing up to 9% and then it decreases with the higher percentage of copper concentration.