Dielectric functions of ferroelectric Bi3.25La0.75Ti3O12 thin films on Si(100) substrates

Ferroelectric Bi3.25La0.75Ti3O12 (BLT) thin films were deposited directly on Si(100) substrates under annealing temperatures of 590 and 700 degreesC. The optical properties of the BLT films have been investigated using spectroscopic ellipsometry at room temperature in the 0.73-6 eV energy range. To model the dielectric functions of the BLT films, the double Tauc-Lorentz dispersion relation was successfully adopted. A four-layer model was used to fit the measured pseudodielectric function in order to deduce the complex dielectric functions. The results show that the annealing temperature mainly affects the dielectric functions of the BLT films beyond the fundamental band gap energy. The volume fraction of air present in the surface rough layer increases with increasing annealing temperature. The fundamental band gap was observed to shift slightly to a higher energy at a high annealing temperature. The difference of the optical properties due to the structure changes testifies the x-ray diffraction spectral results. (C) 2003 American Institute of Physics.