Single Crystal Growth by Czochralski Method in Liquid Encapsulation

Single crystalline growth

Single crystalline growth is a process of growing crystal structures that have only one single crystal orientation and composition. It is a process that is used for the growth of solids with nearly perfect surfaces. One of the most common and successful methods for single crystalline growth is liquid encapsulated pull method (LEV). It is a physical technique which is used to produce single crystals from materials that are usually difficult to single crystallize by other methods.

In the liquid encapsulated pull method, the material needs to be placed in a closed container that is filled with a liquid. The container is then heated either electrically or by a gas burner. As the temperature increases, the material melts and elevates to the top of the container, and forms a single crystal structure. The liquid is used to optimize the cooling rate of the material, so that the crystal formed is of high quality.

This method is used in the production of semiconductor materials, particularly gallium arsenide and indium phosphide. It is also used in other industries, such as steels and ceramics, to produce components that have better quality than what can be obtained with traditional melting and casting processes.

Advantages of this technique are its simplicity, the requirement of smaller amounts of material, and the ability to obtain single crystals of a large size. It is also simple to adjust the temperatures of the container and to monitor the progress of the crystal growth. Since a consistent cooling rate is necessary, if it is not available then the method may produce a crystal structure that is not as perfect as when the cooling rate is controlled. Furthermore, there is a risk that bubbles and dead zones can form in the liquid, leading to inadequate cooling and crystal growth.

All in all, the liquid encapsulated pull method (LEV) is a simple yet effective technique for the production of single crystalline materials from melts. Its advantages include simplicity, low material cost, and large crystal sizes. However, the process is sensitive to fluctuations in cooling rate and requires proper monitoring, since it could lead to an imperfect crystal structure.

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The horizontal gradient freeze method, also known as the single crystal growth method, uses a frozen fluid film shield to directly draw a single crystal. The method is a crystal growth technology. This technology uses a special reaction vessel filled with some high purity source materials, and the high-temperature liquid source materials form a liquid surface film after freezing on the horizontal inner wall of the reaction vessel. Under the combined effects of the inner wall temperature gradient, the single crystal was continuously grown along the horizontal surface.

The horizontal gradient freeze process has the characteristics of low cost, no need for vacuum, good insulation performance and simple operation. Compared with the sealed pull process, it has good repeatability, so it has a good application in the production of single crystals. Its advantage is that the growth process is relatively stable and the size of the single crystal is relatively uniform. This method is also suitable for obtaining single crystals with a small diameter.

In the process of single crystal growth by the horizontal gradient freezing method, the growth rate is generally lower than that of the sealed pull method, and the crystal growth temperature and cooling rate are often lower than those of the sealed pull process. In addition, due to the difficulty of controlling the horizontal gradient freezing process, the presence of defects in the single crystal is often inevitable, so this method is only suitable for lower requirements single crystal.