Tuning of structural, optical and dielectric constants by various transition metal doping in ZnO:TM (TM=Mn, Co, Fe) nanostructured thin films: A comparative study

Abstract ZnO:TM (TM=Mn, Co, Fe) thin films doped with different average doping levels (x=1–9%) were successfully deposited on glass substrates by radio frequency magnetron sputtering technique. The results showed that all the undoped and doped films possessed a strong preferential c-axis orientation with a hexagonal polycrystalline structure. With increased TM doping level, a clear decrease in crystalline quality was observed for all the TM doped ZnO films except for Fe doped ZnO (ZFO) films for the average TM doping level of 3% and 5%. Dense film surfaces with the film thicknesses approximately varied from 73 to 115 nm were obtained. The presence of the Zn, Mn, Co, Fe, O elements and Zn2+, Co2+, Mn2+ and Fe2+ ions were detected in the films. By increasing the TM doping level, the optical band gap was increased for the ZMO films, while decreased for the ZFO and ZCO films as compared with the ZnO films. Among all the films, the highest extinction coefficient in ZCO films as well as the highest refractive index and dielectric constant in ZMO and ZCO films were obtained for average TM doping levels of 1–9, 1, 3 and 5, 9%, respectively. These were likely attributed to increased absorption coefficient, density and polarization of the films by changes in average doping level of TM and TM type.