Structural and optical properties of Zn1-xCoxO and ZnCo2O4 thin films

Thin films of Co substituted ZnO and ZnCO2O4 were deposited on c-axis (0001) oriented Al2O3 substrates using pulsed laser deposition. The XRD results showed all the films were highly (002) oriented with a less intense peak of (311) for ZnCO2O4 thin film. Micro-Raman spectra of ceramic targets showed the modes related to wurtzite ZnO and spinel ZnCO2O4 structures. In thin films of Zn1-xCoxO no modes corresponding to ZnCo2O4 were detected. The intensity of E-1(LO) and multiphonon peak at 584 and 540 cm(-1) respectively, increased with increase in Co substitution. The optical absorption of the films showed that the band gap decreased with increase of Co concentrations at room temperature along with the sub-bandgap absorptions due to d-d transitions of Co2+. Similar sub-bandgap d-d transition was also observed in the absorption spectra ZnCo2O4 thin films. The highest saturated magnetization (0.2 mu(B)/Co) was obtained for 5%Co substituted ZnO.