Ferroelectric microdomains in Ti-diffused LiNbO3 optical devices

Etched hillock density on the -Z plane of a titanium-diffused LiNbO3 optical device was studied as a function of water vapor content in a diffusion atmosphere of oxygen and argon. It was found that the hillock formation depended greatly upon the water vapor content and the type of carrier gas. Furthermore, the shapes of the hillocks in the devices were observed on a microscopic scale. Scanning electron micrographs (SEM) clearly showed the crystallographic shape of steeple-crowned pyramidal hillocks. The shape of the steeple (i.e., the core) was compared with a cross-sectional view of an etched LiNbO3 single-crystal c-axis fiber, and it was revealed that the core was a microdomain whose polarization was opposite that of the outer matrix. The mechanisms which cause the microdomains to form during the Ti-diffusion process are also discussed.