Raman spectroscopy of V and Co doped ZnO ceramics and thin films

Lattice dynamical and electronic transition changes due to V and Co doped ZnO have been investigated using optical techniques. Vanadium and Co doped ZnO pellets were prepared using conventional ceramic processing route and thin films were fabricated by pulsed laser deposition. Raman spectra of Zn1-XVXO targets showed many additional peaks in the range of 230 to 350 cm(-1) and 750 to 900 cm(-1). Integrated intensities of these additional modes decreased with increase of temperature as similar to the host ZnO modes, which precludes electronic Raman scattering to be the origin. Raman peaks for stoichiometric Zn-3(VO4)(2) and Zn2V2O7 compounds also had additional peaks that can be attributed to the secondary phases formed in the compositions of Zn1-XVXO. Raman spectra of Zn1-XCoXO showed no additional modes besides ZnO modes, however, the intensity of the second order peak at 540 cm(-1) was increased due to Co doping. Thin films of Zn1-XCoXO exhibited highly c-axis orientation deposited on (001)Al2O3 substrates. 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+.