Controlling crystal quality and orientation of pulsed-laser-deposited BaTiO3 thin films by the kinetic energy of the film-forming particles

The deposition of BaTiO3 thin films by pulsed excimer laser radiation (248 nm) on Pt/Ti/Si(111) and Pt/Ti/Si(100) substrates is investigated as a function of the processing variables laser fluence, processing gas pressure, and target-to-substrate distance under conditions of temporal and spatial properties of the involved vapour and plasma states. The kinetic energy of the species in the laser-generated plasma, as measured by time-of-flight optical emission spectroscopy and time-of-flight quadrupole mass spectrometry, is described as a function of the pressure of the processing gas, the distance from the target, and the laser fluence. The influence of the kinetic energy of the film-forming particles on the crystalline structure, defects, and orientation, and on the resulting electrical properties of the films is investigated. X-ray diffraction measurements and polarisation-dependent micro-Raman measurements reveal a c-axis orientation normal to the substrate surface, in the case of high particle energy (> 50 eV), whereas at low kinetic energies (< 30 eV) a [111](pc) or [110](pc) orientation is preferred. The ferroelectricity and the dielectric constant of the films, determined by impedance measurements, decrease with increasing kinetic energy of the film-forming particles from epsilon(r) = 1000-2200 to epsilon(r) = 200-700. This decrease correlates with the change of the orientation and with an increasing lattice constant of the films, indicating that particles with high kinetic energies produce crystal defects and stress in the growing film.