It was noted that the dislocation density of conventional liquid encapsulated Czochralski crystals of 7.5 to 10cm in diameter was too high to reveal the dislocation generating conditions. Therefore, the growth of dislocation-free crystals was required before moving to larger crystal sizes. In order to reduce the dislocation density, crystals were grown by using the As-ambient liquid encapsulated Czochralski technique with a small temperature gradient in the pulling direction. An etch pit density of the order of 1000/cm2 was obtained at the center of a 2cm-diameter crystal. The etch pit density distribution and the crystal shape in the pulling direction were found to be related in the case of crystals with a low etch pit density. This showed that crystal shape control was necessary in order to obtain crystals with a lower etch pit density. However, the etch pit density distribution perpendicular to the pulling axis was W-shaped. Although the temperature gradient in the pulling axis was low, dislocations which were considered to be generated by an excessive radial thermal gradient were present in the crystals.

K.Usuda, T.Fujii: Journal of Crystal Growth, 1995, 151[1-2], 13-20