Czochralski Growth of Low-Dislocation-Density Zinc Tungstate Crystals

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Abstract
Zinc tungstate crystals were grown by the Czochralski method and the effect of growth parameters on crystal perfection was studied. Of the (010) and (100) slip planes, Berg‐Barrett photographs showed that the (100) slip plane appeared to be the most active during crystal growth. Observations made on crystals grown in a steep temperature gradient showed that strain due to thermal gradients was responsible for the high dislocation densities in these crystals. Studies on seeding showed that if no widening occurred, then the perfection of the region of the crystal after seeding was much higher than the seed; the changes in temperature employed to widen the crystal gave rise to very high dislocation densities. X‐ray examination verified the observations made by chemical etching. Crystals grown under nearly isothermal temperature conditions provided material with dislocation densities between 0 and 500/cm2. These crystals propagated with facets at the solid‐liquid interface which gave rise to impurity distributions similar to those observed in semiconductor crystals. The conditions for growing low‐dislocation‐density Czochralski crystals of zinc tungstate are similar to those for growing low‐dislocation‐density semiconductor crystals.

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