Growth of Co-doped ZnO thin films exhibiting room temperature ferromagnetism using a low-cost spray pyrolysis technique

Cobalt (Co)-doped zinc oxide (ZnO) diluted magnetic semiconductor thin films were grown using a low-cost spray pyrolysis technique. X-ray diffraction (XRD) studies show that the films crystallize in the pure wurtzite structure. No evidence of the formation of secondary phases like Co clusters, CoO or Co3O4 were detected from XRD studies. Scanning electron microscopy studies show uniform growth over the substrates and energy dispersive analysis of X-ray studies confirm the presence of Co in ZnO. The absorption bands peaked at the wavelength similar to 658, 613 and 567 nm in the optical transmission spectra show that the Co enters the tetrahedral sites of the wurtzite structure in the desired Co2+ oxidation state. The strong optical absorption in the band tail region indicates the existence of magnetic ion-induced charge-transfer states (CTSs) just below the band edge. The photoluminescence from ZnO is found to be completely quenched on Co doping due to the occurrence of CTSs. Magnetic studies show that all the films possess ferromagnetism at room temperature with Curie temperature well above the room temperature. The grown films have potential applications in spintronic devices.