Raman spectroscopy study of ZnO-based ceramic films fabricated by novel sol–gel process

Abstract

The ZnO-based ceramic films doped with different dopants were prepared by a novel sol–gel process. The phase composition of the films was determined via X-ray diffraction analysis. The influence of the dopants on the residual stress, carrier concentration and the secondary phases was studied by means of Raman spectroscopy. Raman spectra show that the E 2 phonon frequency shifts 3–6 cm −1 to lower wavenumbers, whereas the A 1(LO) mode shifts 3.2–6.1 cm −1 to higher wavenumbers when the films were doped with Bi 2O 3, Sb 2O 3, MnO, Cr 2O 3, Y 2O 3 and Al 2O 3, indicating that both the tensile residual stress and the free carrier concentration were increased with doping. The larger stress is considered to originate from the lattice distortion, which was caused by the substitution of the doping ions for Zn 2+, and the lattice mismatch between the ZnO crystals and the interfacial phases. The secondary phases were affected markedly by both Y 2O 3 and Al 2O 3. The intensity and the position of Raman bands of Zn 7Sb 2O 12 and ZnCr 2O 4 phases changed obviously. The films showed remarkable nonlinear voltage–current characteristics, but the nonlinear coefficient of the films decreased evidently as the addition of Y 2O 3 or Al 2O 3.