Development of a GaN crystal manufacturing device

Thursday, 23 January, 2020

Development of a GaN crystal manufacturing device

Researchers at the Japan Science and Technology Agency (JST) have announced the successful development of a high-quality bulk gallium nitride (GaN) growth device. Development towards commercial applicability was carried out by the Innovation and R&D Division of gas manufacturer Taiyo Nippon Sanso from August 2013 to March 2019, based on the research of Professor Akinori Koukitsu of the Tokyo University of Agriculture and Technology.

Gallium nitride crystal is a semiconductor widely used as a blue light-emitting diode, but it is also well suited to use as a power device material in equipment for high-speed switch operation and high-voltage, high-current applications. GaN crystal is said to be far superior to silicon crystal, the current mainstream material.

The majority of GaN crystal substrates used in electronic devices are manufactured using the hydride vapour phase epitaxy (HVPE) method, in which a metallic chloride gas and a non-metallic hydride gas react on a substrate to epitaxially grow a semiconductor crystal on the substrate. It is difficult to produce thick GaN crystals using the HVPE method due to distortions in the crystal, and GaN crystals are grown on a seed crystal heterogeneous substrate and repeatedly peeled off at a thickness of less than 1 mm for use. For this reason, commercially practical manufacturing of GaN crystals has not been possible thus far on the basis of cost and crystal quality — particularly in light of the pre- and post-work required in the process, such as cleaning the furnace.

Sample of GaN crystal with 2″ diameter. Front side: Transparent, no unnecessary polycrystals are generated on the wafer edge. Back side: Since the surface is smooth, the fluorescent light is reflected. Image ©Tokyo University of Agriculture and Technology.

Taiyo Nippon Sanso has advanced the HVPE method to develop a GaN crystal production system that achieves high-speed, high-quality, continuous growth through the tri-halide vapour phase epitaxy (THVPE) method utilising a gallium trichloride-ammonia reaction system. The THVPE method succeeds in forming high-quality crystals at a high-speed growth rate three times faster than current conventional methods, with only one-fifth the current rate of dislocation defects. The method also offers many cost advantages over current techniques, such as not deteriorating quartz glass tube as the reactor, preventing reduction of crystal growth area and reducing the occurrence of unnecessary polycrystals.

If the THVPE technique can be further developed to achieve production of thick GaN crystals, it will allow the mass-production of GaN crystal substrates through slicing. The technique thus holds strong promise to achieve a breakthrough in the development of low-cost, high-performance GaN devices.

Top image caption: The THVPE crystal growth furnace. Image ©Taiyo Nippon Sanso Co.

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