Crystal pulling using acrt

A method is formulated to apply the "Accelerated Crucible (and Crystal) Rotation Technique" to the Czochralski method in order to produce crystals of improved homogeneity. The pulling velocity has to be adjusted to the change of the surface of the melt, which is caused by the variation of centrifugal forces during periodic acceleration and deceleration of the crucible. An analytic expression is derived connecting the angular velocity of the crucible with the change in shape of the liquid surface. This is verified by simulation experiments. The simple technical realization of automatic level (and diameter) control of the pulled crystal is indicated, and the maximum size of the growing crystal (which is limited by stresses acting on the seed crystal) is estimated. © 1980.