Microdomains control in quasi-stoichiometric LiNbO3 wafers

In this work is presented a study on the surface microdomain formation in quasi-SLN Z-cut 3" crystals, with an accurate control on both the composition and on the wafering process. The UV absorption edge has been measured and correlated with the crystal composition, showing the edge shift towards shorter wavelengths. The coercive field has been measured as a function of temperature and it has been found lower in the quasi-SLN substrate if compared with the congruent crystals. The microdomain formation at wafer level can be controlled and avoided by appropriate composition choice as well as wafer mechanical and thermal treatments, and is checked by chemical etching and subsequent optical inspection. It has been found that quasi-SLN crystals with 49.82 Li2O mol% content could present microdomains formation even after the photoresist process. On the other side, quasi-SLN crystals with 49.72 Li2O mol% content seem to be more stable for both photoresist and Ti diffusion process for waveguide fabrication. A careful control on LiNbO3 composition and wafer surface quality allows one to find the proper compositional window for the realization of various advanced optical and electro-optical devices.