Abstract
Unstable growth of TiO_2 ribbon and boule single crystals, grown by the edge-defined, film-fed growth (EFG) method, are characterized by periodic change of ribbon width and spiral growth, respectively. Those phenomena occur under the condition that the die top temperature is higher than that at the uniformly shaped crystal growth. Features of this growth are that the temperature distribution on the die top is largely dependent on the location of the growing crystal which absorbs thermal radiation and shields the heat transfer from the die top. In the case of periodic change of ribbon width, higher die top temperature generates meniscus receding and ribbon width decreases. Resultantly, die top temperature is decreased by acceleration of heat radiation from die top. This relation causes the vibration of die top temperature and ribbon width changes periodically. Spiral growth has the same origin as the periodic change of ribbon width. The asymmetric temperature conditions on the die top is maintained by the movement of the meniscus and growing crystal. As a result, the asymmetry persists and a spiral is continuously formed.
