Bulk PPKTP by crystal growth from high temperature solution

Periodically-poled ferroelectric crystals show unprecedented efficiency and properties otherwise impossible to obtain. Unfortunately, the sample thickness obtainable today limits their use to low and moderate power application. With the aim of increasing the size of periodically domain-structured crystals with a controlled and regular grating period, we proposed an epitaxial growth process using seeds made of thin plates domain engineered by electric field poling. We demonstrated this process with the ferroelectric crystal KTiOPO4 (KTP) which is one of the most promising candidate materials for that purpose. The poling step requires a sample exhibiting (001) and (001̄) faces, so that the growth step has to be performed onto these faces. This constraint is a difficulty to circumvent as these faces are not present in the standard equilibrium morphology. It is then necessary to find the growth conditions enabling to work below the roughening temperature of these faces. By using a high temperature solution method, the so-called “flux method”, and by choosing an appropriate chemical composition of the flux solution, we obtained periodically domain-structured KTP layers with thicknesses up to 800 μm and regular periodicity onto (001) and (001̄) faces of the initial PPKTP seeds.

► We have proposed a two step process to grow periodic domain-structured KTP layers. ► The layers were grown onto c faces of an initial PPKTP seed. ► 4KPO3:2KF solvent allowed the growth to be performed below TC and TR of c faces. ► The crystalline quality of the grown layer and substrate are very similar. ► This technology is suitable for template-growth of engineered nonlinear structures.