Composition dependence of electrooptic property of epitaxial (Pb,La)(Zr,Ti)O₃ films

The Zr/Ti ratio dependence of refractive index and electrooptic coefficient of epitaxial (Pb,La)(Zr,Ti)O₃ (PLZT) films were investigated. PLZT films were fabricated on La-doped SrTiO₃ (La-STO) substrates by a chemical solution deposition (CSD) method. Optical properties in TE-and TM-modes were measured individually using a prism coupling method. The refractive indexes both in TE-and TM-modes were as large as that of the polycrystalline film, and increased with increasing Ti/(Zr + Ti) ratio. The refractive index in TE-mode was larger than that in TM-mode because the PLZT films received compressive stress from the La-STO substrates due to lattice mismatch. The refractive index in TM-mode almost linearly decreased with increasing applied an electric field while that in TE-mode slightly increased and saturated around at 200 kV/cm. The Pockels coefficient in TM-mode r₃₃ showed large change for compositions, while that in TE-mode r₁₃ showed little change. The maximum Pockels coefficient r_c of 156 pm/V was obtained for the epitaxial PLZT film with Ti/(Zr + Ti) ratio of 50%.