SPIRAL GROWTH OF RUTILE SINGLE-CRYSTAL BOULES IN THE EDGE-DEFINED, FILM-FED GROWTH-PROCESS

Spiral growth of rutile crystal boules, obtained by the edge-defined, film-fed growth (EFG) method, is analyzed using the results of radiati ve spectral measurements of the die top during crystal growth. The obs ervation of spiral growth is connected with the absorption of thermal radiation in the growing crystal which shields the heat transfer from the die top. In such a case, the temperature distribution on the dic t op is largely dependent on the location of the growing crystal on the die top. The meniscus tends to move to an area free from growing cryst al on the die top. This results in an asymmetry of the temperature dis tribution which is difficult to change and a spiral crystal results.