Photo-induced and electrooptic properties of (Pb,La)(Zr,Ti)O₃ films for optical memories

Abstract

Photo-induced hysteresis changes and electrooptic effects in sol-gel Pb(Zr,Ti)O₃ (PZT) and (Pb,La)(Zr,Ti)O₃ (PLZT) films have been studied in an effort to evaluate these materials for optical memory applications. The films exhibit two distinct, but related, types of photo-induced changes in their hysteresis behavior: 1) a photo-induced change in the coercive voltage and 2) a photo-induced suppression of the switchable polarization. Both types of photo-induced hysteresis changes are due to trapping of photo-generated charge carriers at sites which minimize internal depolarizing fields. The photo-induced changes are reproducible and stable and are, thus, suitable for optical memory applications. In addition, polarization-dependent changes in the refractive indices can be the basis of a nondestructive optical readout technique. To characterize these electrooptic effects, a waveguide refractometry technique has been used to independently determine field-induced changes in the ordinary and extraordinary indices. For an applied field sufficient to saturate the ferroelectric polarization (E = 125 kV/cm), the ratio of the extraordinary to ordinary index change (Δn_e/Δn_o) of a Pb(Zr_0.53Ti_0.47)O₃ film was found to be −4/1, leading to a net birefringence change [Δ(n_e −n_o)] of −0.21.

Keywords:

• Ferroelectric films
• photoferroelectric
• electrooptic
• optical memory