High-purity semiconductor crystals made of gallium oxide, for example, are required for power electronics in electric cars or in photovoltaics. Researchers from Japan and Germany have now developed a method to produce such crystals without crucibles using a laser-based process. The team at the Fraunhofer Institute for Laser Technology ILT in Aachen has developed a process-optimized high-performance optical system for this purpose, which is used in conjunction with a 20 kW laser.
With a melting point of around 1,800 °C, gallium oxide (Ga2O3) can be grown from the melt. If the heat is supplied in the form of radiation rather than via a crucible, the polycrystalline starting material can be remelted into a high-purity single crystal. The optics for high laser powers must be carefully designed and cooled, as even small losses of less than one percent can lead to the destruction of the optics during prolonged use.
At the Fraunhofer ILT in Aachen, a water-cooled high-performance optic was developed specifically for the LDFZ process and then transferred to the project partners in Japan for testing. Initial results are very promising. It was possible to grow crystals with a diameter of up to 30 mm - the largest gallium oxide crystals ever produced using a crucible-free growth process
