【World Express】Fabrication of Ga₂O₃ Single Crystal Without Using Precious Metal Crucible

The external sales of Ga₂O₃ chips with 2-inch diameter are also planned.

Crystal growth technology is called OCCC method

Source: C&A,TOHOKU UNIVERSITY

  In April 2022, Kei Kamada, president of C&A, a start-up company of TOHOKU University, and Professor Akira Yoshikawa (also serving as the Joint Research Center for Future Science and Technology of TOHOKU University) of the Materials Research Institute of TOHOKU University announced that the new method for crystal growth without using "precious metal crucible", and gallium oxide (Ga₂O₃) single crystals with a maximum diameter of about 5cm were successfully produced. The company said. It will be possible to cultivate high-quality crystals while reducing production costs.

  The energy saving performance of gallium oxide is 3400 times higher than that of silicon (Si) and 10 times higher than that of silicon carbide (SiC). Moreover, since the solution crystal growth is possible, the growth rate of gallium oxide is 10~100 times faster than that of SiC. It will be possible to produce a large number of crystals at one time, which is expected to reduce the cost of Ga₂O₃ substrate.

  However, until now, crystal growth methods have used "crucibles" containing expensive precious metal "iridium" to keep the melt. This makes that it is difficult to reduce the cost of production and oxygen defects, which become problems to be solved.

  The research team has developed a new crystal growth device and technology called OCCC (Oxide Crystal growth from Cold Crucible) without "crucible"  method. Specifically, the Ga₂O₃ raw materials are filled in a special container with gaps, and the high frequency coil is used to generate a magnetic field to directly heat the Ga₂O₃ raw materials. If the output of high-frequency magnetic field is increased, gallium oxide raw materials will be melted. At this time, the temperature between the raw material melt and the water-cooled container becomes suitable for sintering, and the peripheral gallium oxide solidifies, acting as a "crucible".

  In order to realize Skull Melt's crystal growth method, C&A independently developed a high-frequency heating device as a heat source. In such an environment, the crystal seeds can grow by contacting the melt, and then large diameter gallium oxide crystals can be produced.

  In this experiment, high quality Ga₂O₃ single crystal with a maximum diameter of about 5cm was produced. C&A plans to use the results of this research to produce a gallium oxide substrate with a diameter of 2 inches, so that marketing could be realized as soon as possible. In addition, by optimizing the crystal growth conditions, the substrate with lower crystal defects and larger size will be realized.