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Bridgman–Stockbarger single crystal growth is one of the important process for the fabricating high-efficiency, high-quality optical and electronic materials. The basic principle of the process originated from the work of Percy W. Bridgman and Wilson D. Stockbarger，who independently studied and perfected the process. This method is based upon the control of the thermal gradient that is used in the solidification of a single crystal. The Bridgman–Stockbarger method is used extensively for the growth of single crystal materials including quartz, Ge, Si, GaAs and indium phosphide.
In the Bridgman–Stockbarger technique, the single crystal is grown inside of a boat rotation assembly, which is then placed inside a vacuum or controlled atmosphere furnace. The slow motion of the assembly allows the molten material to solidify in a graded thermal gradient and this gradient more closely approximates the thermal gradients encountered in nature. This allows the atoms to form in such a way as to produce a single crystal, with a minimum number of defects, and to have good optical properties.
The boat rotation assembly consists of a graphite or molybdenum boat, which holds the growth material, and a spinning device, which rotates the boat during the growth cycle. The entire device is contained in a vacuum or controlled atmosphere environment to prevent contamination of the growing crystal. The molten material is heated using an electric resistance heating element and the temperature of the furnace is well controlled by an accurate temperature controller.
The single crystal growth cycle begins by adding the growth material (quartz, Gase crystalline silicon, etc.) to the boat assembly. The growth cell is then placed in the vacuum or controlled atmosphere furnace. The temperature is increased to the melting point of the material and the boat is slowly rotated throughout the growth process.
As the heated material begins to cool, the thermal gradient moves incrementally through the molten material crystalizing it from the bottom up. If the thermal gradient is properly controlled, the molten material crystallizes in a single crystal formation with a minimum number of defects. When the crystal has reached its full growth potential, the furnace is allowed to cool to room temperature. The resulting single crystal is removed from the boat and is inspected under a microscope.
The Bridgman–Stockbarger single crystal growth method has proven to be very reliable and produces materials with a high degree of optical and electronic integrity. The process is also cost effective, since production of a single crystal can be completed in a relatively short period of time, and the technique is easily scaleable. As with all crystal growth methods, production of a high quality single crystal requires a great deal of expertise. It is important to have a team of experienced operators who understand the subtleties of the technique in order to maximize the yield and quality of the material.
