The structural and optical properties of ZnO thin films prepared at different RF sputtering power

ZnO thin films were prepared on glass and Si(100) substrates by RF sputtering. The thickness, crystallinity, and the optical properties of the films were observed to vary with the RF power used. All the films exhibited preferred c-axis oriented (002) phase of wurtzite structure. The values of d-spacing for ZnO films were higher than those of the d-spacing for ZnO powder, suggesting that all the ZnO films experienced tensile strain. Good optical transmittance of 70–88% in the visible range has been observed in all the films. The PL spectra showed a dominant UV emission peak that shifted from 3.31 eV to 3.17 eV with decreasing RF power of the sample. The Raman lines around 433.26 cm^-1 and 573.72 cm^-1 attributed to E2 (high) and A1 (LO) respectively, were observed for all the ZnO films. The presence of tensile strain in the ZnO films was evident from the results of Raman spectra and XRD data. Defects due to oxygen vacancy in the prepared ZnO films were manifested in the PL and Raman spectra characteristics.