Microstructure and physical properties of ZnCoO films prepared by pulsed DC magnetron sputtering

We investigated the microstructure, optical, electrical and magnetic properties of ZnCoO thin films, which were prepared by asymmetrical bipolar-pulsed DC magnetron sputtering as a function of substrate temperature. The structural properties of ZnCoO films were characterized with high resolution X-ray diffraction. The X-ray diffraction patterns of the ZnCoO films showed a strong ZnO wurtzite phase with (002) preferential orientation. The average crystallite size was 23 nm to 35 nm, which was calculated from full width at half maximum of X-ray diffraction results. The optical transmittance of the films which were deposited above 300degC substrate temperature was over 80 % in the visible region. The absorption bands were observed due to the sp-d interchange action by Co²⁺ complex ion and d-d transition in the region from 500 nm to 700 nm. The electrical resistivity of the films was below 10^-1 Omegacm above 300degC. The magnetic properties of the films were analyzed by the alternating gradient magnetometer at room temperature. All the films are exhibited the ferromagnetic nature. The high conductivity and room temperature ferromagnetism of ZnCoO films above 300degC suggested that the possibility for the application to diluted magnetic semiconductors.