A comparison of the optical properties of amorphous and polycrystalline PZT thin films deposited by the sol-gel method

Stoichiometric Pb(ZrxTi(1-x)O3) (PZT) thin films deposited on Si(1 0 0) substrates have been prepared by the sol-gel technique. Two sets of films of amorphous and polycrystalline, containing 20%, 30%, 50%, and 60% Ti, were prepared and investigated. The microstructures and surface morphologies of the films have been studied by X-ray diffraction and atomic force microscopy. The optical properties were studied by spectroscopic ellipsometry (SE) in the UV-visible region. Using a four-phase fitting model, the refractive index n and extinction coefficient k was obtained by analyzing the SE spectra. The optical band gap energies Eg for these films were determined under the assumption of a direct band-to-band transition. The results show that the refractive index, extinction coefficient, and band gap energy of the films show a systematic variation with compositions and microstructures. The optical band gap energy of the amorphous PZT films shift to high energy is mainly due to the quantum-size effect.