Hot Zone Design

Hot Zone Design

My many years of experience in crystal growth have taught me that the design of the hot zone in which the crystal is grown is one of the most critical factors in the successful growth of high quality crystals.  In a typical melt growth system (Czochralski, Kyropoulos, Bridgman, etc.) the solid-liquid boundary defines the growth interface.  Heat flows in one direction perpendicularly to this surface and mass (in the case of segregating solutes) flows in the opposite direction.  The temperature gradient at the growth interface (which is primarily determined by the hot zone design) is crucial to determining interface stability. Some materials require a very high temperature gradient in order to stabilize the growth interface against constitutional supercooling (see reference 10 under publications). Others require a low gradient to minimize chemical reactions between the melt and the crucible (see reference 7 under publications).

Equally important to the hot zone design, and critically connected to it, is the chemistry of the process. The reaction between the melt, crucible and atmosphere is often overlooked. Stoichiometry of the melt constituents (their exact chemical ratio), as well as impurities, is also important. Some systems actually require the presence of particular impurities in order to grow a high quality crystal.