Scientists produce superior gallium oxide semiconductors with double current capacity

Gallium oxide (Ga₂O₃) is a semiconductor material that could make electronic devices much more energy-efficient than current silicon-based technology. Electronic diodes require two types of semiconductor layers to function properly, negative-type (n-type) and positive-type (p-type) layers. Scientists could reliably produce n-type gallium oxide layers but struggled to create stable p-type layers because gallium oxide's crystal structure naturally resists the atoms needed for these layers. This limitation resulted in gallium oxide semiconductors with poor performance and reliability issues. 

Now, researchers at Nagoya University in Japan have solved this manufacturing challenge and created the first functional pn diodes using gallium oxide. Their method, published in the Journal of Applied Physics, enables the use of gallium oxide for improved semiconductors and energy efficient devices. In addition, these new pn diodes can carry twice as much electrical current as previous gallium oxide diodes. 

Quest to produce a stable p-type gallium oxide layer 

Pn diodes are made by joining p-type and n-type semiconductor materials which creates a connection point that controls electrical flow. These diodes can handle high voltages and are found in most electronics. However, current silicon-based pn diodes waste a lot of energy as heat, especially in energy intensive applications such as electric vehicles and renewable energy power grids.  

Gallium oxide pn diodes can handle twice the current capacity of previous gallium oxide devices and waste less energy than silicon-based diodes. This makes them ideal for demanding applications and translates to decreased cooling requirements, better energy efficiency in high-power systems, and lower operating costs. 

The problem was that gallium oxide's crystal structure easily accepts the atoms needed to create n-type layers but rejects the atoms required for p-type layers. Previous methods to force them in either failed or required temperatures that destroyed the material. Without both types working together, gallium oxide remained limited for practical applications. 

To address this, the researchers injected nickel atoms into the gallium oxide layer by shooting individual atoms at high speed into the surface of the material. They then heated the material twice, first at 300°C with activated oxygen radicals (oxygen atoms that have been given extra energy using proprietary plasma treatment) and then at 950°C in oxygen gas. This converted the embedded nickel into nickel oxide and properly integrated it with the gallium oxide crystal structure.  

Future impact and innovation 

“Since this method uses standard industrial equipment and processes, it can be scaled up for mass production,” Professor Masaru Hori from the Center for Low-Temperature Plasma Sciences at Nagoya University highlighted. “The implications for future energy efficiency and costs are substantial, particularly for electric vehicle and renewable energy industries.” 

The gallium oxide semiconductor market is projected to reach 14.9 billion yen annually by 2035. This new manufacturing process solves a fundamental problem that previously limited industrial applications. Nagoya University spin-off company NU-Rei is now working to bring these advances to market.