Growth habits of 3 and 4-inch langasite single crystals

A macro defect-free langasite (La₃Ga₅SiO₁₄) crystal in 4″ diameter was grown along [0 0 0 1] and [0 1 1̄1] directions by the Czochralski technique. The interface during growth was a faceted plane of (0 0 0 1) for the [0 0 0 1] growth while (0 1 1̄1) interface plane was decomposed into (0 0 0 1) and (0 1 1̄1) making a rough interface for the [0 1 1̄1] growth. For the latter growth, the interface was convex toward the melt and the degree of convex was determined by the mode of dissolution of these two planes which was controlled by the radial and axial temperature gradients in the melt near the interface. The volume defect that was initiated at secondary phases occurred when the melt was away from the congruent melt composition. The homogeneity in composition was discussed in association with the relationship between SAW velocity, d-spacing of a specific plane and chemical composition. The congruent melt composition is close to a stoichiometric composition and was found to be a slightly rich in Ga component by examining the compositional variation in both crystal and residual melt during growth. The simple and easy way by use of bulk wave was demonstrated for the measurement of the uniformity of wafers fabricated from grown crystals.