Raman spectroscopy on BaTiO3 ferroelectric thin films deposited by a hybrid DC-field enhanced PLD-process

Raman spectroscopy is employed for structural characterization of BaTiO3 ferroelectric thin films, deposited by a hybrid DC-field enhanced pulsed laser deposition (PLD)-process. Pulsed excimer laser radiation (KrF, lambda=248 mn, tau=25 ns) is used for material removal from a sintered BaTiO3-target in an 02 processing gas atmosphere (pressure p(O2)about 1 * 10(exp -1) mbar) with subsequent deposition on a substrate. Additional energy is supplied to the laser-induced plasma via a system of two concentric ring electrodes lying on different electric potentials (difference delta V up to several hundred V), leading to further activation of the plasma and ignition of a DC-discharge in the processing gas atmosphere. Micro-Raman spectroscopy is performed with Ar+ laser radiation (lambda=488 mn), using a microscope unit to achieve a high spatial resolution in the range of 1 gm. The Raman spectra of the BaTiO3 films show peaks typical for the tetragonal/cubic Perovskite structure. Polarization-d ependent measurements reveal a mean c-axis orientation normal to the substrate surface, regardless whether a DC-field is applied or not. Using low DC-bias voltages (delta V=50 V) allows lowering the substrate temperature without affecting the crystal quality of the films, as determined from the full width at half maximum (FWHM) of the Raman peaks, which is a measure for the crystal quality. High DC-bias voltages (delta V=700 V), however, lead to amorphous films. The dielectric constant of the BaTiO3 films is strongly correlated to the crystal quality.