Using a Bridgman Furnace for Crystal Growth

Bridgman furnaces are a type of industrial furnace designed to promote single crystal growth. The furnace uses a method attributed to the American physicist Percy Williams Bridgman.

How Bridgman Furnaces Work

Bridgman furnaces contain a strong temperature gradient, which is used to promote the growth of single crystals.

Pre-synthesized material is emptied into a crucible, which is then passed down the temperature gradient (from high to low temperature). Throughout its journey the material goes from a fully melted state then begins to slowly solidify into one single crystal.

Another technique exists which can be seen as an extension to the Bridgman method - the Stockbarger method. The Stockbarger method has three separate temperature zones within the furnace:

  • Zone 1 has a temperature greater than the materials melting point
  • Zone 2 has a temperature that is intermediate
  • Zone 3 has a temperature less than the materials melting point

The Bridgman method and Stockbarger methods are so similar the terms are often used interchangeably. In addition, many Bridgman furnaces use a Stockbarger method as it provides greater temperature gradient control.

In the hottest section of the Bridgman furnace the pre-synthesised material is completely melted in a crucible. Crucially, this crucible contains a single crystal, which acts as a point of nucleation (seed), to ensure single-crystal growth during the process.

The crucible is then moved down the temperature gradient. When the surrounding temperature drops below the material’s melting point crystallization begins to occur around the single crystal seed. By the time that the crucible has reached the bottom of the temperature gradient the melted material will have converted into a solid single-crystalline ingot.

The Bridgman method is frequently used to create the low-flaw crystals required by the semiconductor industry, such as GaAs, which are hard to produce using different methods.

Thermcraft’s Bridgman Furnaces

Thermcraft produces and develops a wide range of industrial furnaces. From ‘standard’ furnaces for common industrial processes to custom built furnaces for specific applications, including furnaces for the Bridgman method.

Thermcraft has experience in building Bridgman furnaces, having built customized vertical Bridgman furnaces for clients.

One Bridgman furnace, developed and constructed by Thermcraft, was built with geared stepper motors to provide total control over the transportation of the sample and rotation of the furnace.

The furnace contained three temperature zones, as per the Stockbarger method, with a maximum temperature of 1,200 oC. The furnace was built with a PLC user interface, allowing the furnace to be easily operated.

Thermcraft has the expertise and equipment to develop and construct custom Bridgman furnaces to specification. If you need a Bridgman furnace and can’t find an ‘off-the-shelf’ solution then get in touch with Thermcraft – one of their engineers will be able to help.

This information has been sourced, reviewed and adapted from materials provided by Thermcraft Inc.

For more information on this source, please visit Thermcraft Inc.

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