Improvements of uniformity and stoichiometry for zone-leveling Czochralski growth of MgO-doped LiNbO3 crystals

The zone-leveling Czochralski (ZLCz) technique is a continuous feeding process and can be used for the growth of near-stoichiometric lithium niobate (SLN) single crystals. However, the finite crucible length can cause the variation of the zone length and thus the composition and stoichiometry, especially in the growth of a large diameter crystal. To solve the problems, several approaches were proposed for the growth of 4 cm-diameter 1 mol% MgO-doped SLN. The modification of the hot zone to minimize the zone variation was found useful for the uniformity, but the stoichiometry was inadequate even with the zone composition up to 60 mol% Li2O. A Li-excess feed was further used and a good Li/Nb ratio was obtained. Adding K2O (16 mol%) into the solution zone was useful as well, but it was inferior to using the Li-excess feed. In addition, a much lower growth rate was needed for getting an inclusion-free crystal.