Eco-friendly GaN semiconductor production boosts crystal quality

Researchers from Nagoya University have developed a technique that enables gallium nitride (GaN) semiconductors to be grown without ammonia, a toxic chemical that requires a sophisticated detoxifying system before it can be released into the atmosphere. The new technique is environmentally friendly and allows for the efficient and high-quality growth of crystals at a lower cost. It also enables scientists to make semiconductors more efficiently, with a reduced need for raw materials and power.

GaN is a compound made up of gallium (Ga) and nitrogen (N) that acts as a semiconductor. GaN semiconductors are used in mobile base stations, fast charging power supply adapters, microwave and millimetre wave communications, imaging, radio astronomy, power switching and radar systems, because of their ability to handle high voltage and current.

The most commonly used technique for commercial production of GaN films is metal organic chemical vapour deposition (MOCVD), which uses ammonia (NH3) gas as the source of the nitrogen added to the Ga. However, the rate at which ammonia is broken up in this process, known as the decomposition efficiency, is low. As a result, a large consumption of ammonia is necessary.

“Ammonia is a very toxic and corrosive gas if inhaled that can cause severe damage to the eyes, skin and respiratory system. Because it is so toxic, much of the ammonia has to be detoxicated and disposed of unused, requiring a lot of energy. This is a large part, up to half, of the total production cost,” said Dr Arun Dhasiyan, a corresponding researcher.

The researchers activated nitrogen, a readily available gas in the atmosphere, by applying high-frequency power (100 MHz) to one of the electrodes. Using this patented technique, the researchers developed a low-cost, high-quality GaN material for semiconductor devices.

“Our method solves three problems of GaN growth. It enables the growth of GaN semiconductors at lower temperatures (about 800°C compared to over 1150°C); it uses nitrogen and hydrogen gas instead of ammonia gas, saving on raw materials and lowering the production cost; and also cuts out the extraction of nitrogen from ammonia step, making the process faster at lower temperatures,” Dhasiyan said.

The new crystal growth method could replace the conventional method, as it is easy to industrialise and produces GaN semiconductors with fewer impurities. The researchers expect the development of new technology to enhance low-power consumption GaN semiconductor devices, resulting in more efficient power devices. At present, industrial equipment for large-diameter substrates of 150–300 mm is required for applications to power devices and low-cost LEDs. The researchers installed a 300 mm diameter REMOCVD system to test the large-scale production; they found that the high growth rate and crystal quality of GaN using REMOCVD could replace the MOCVD method.

“We have grown GaN, aluminium nitride, indium nitride and aluminium indium nitride layers using the REMOCVD method and found that it is very effective to grow all of these commonly used semi-conductor materials at much lower temperatures than those of the MOCVD method without using any ammonia gas,” Dhasiyan said.

The research findings have been published in the journal Scientific Reports.

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