Mitsubishi Electric Corporation has demonstrated a method to significantly suppress frequency dispersion in gallium nitride (GaN) transistors by using GaN substrates instead of conventional silicon carbide (SiC) substrates. The research addresses a longstanding challenge in high-frequency GaN devices, where crystal defects can cause variations in electrical characteristics during operation. By reducing these effects, the company has demonstrated more stable transistor performance, potentially enabling smaller, more efficient RF systems with lower power consumption.
GaN transistors are increasingly used in applications requiring high output power and efficiency, including 5G/6G communication base stations, radar systems, and industrial microwave heating equipment. One emerging application is microwave heating for chemical recycling, where high-frequency energy is used in processes that convert waste plastics back into chemical raw materials.
Conventional GaN transistors typically use a GaN epitaxial layer grown on a SiC substrate, which provides high thermal conductivity and effective heat dissipation. However, differences between the substrate and epitaxial layer materials introduce crystal defects during the growth process.
These crystal defects impede electron movement during high-frequency operation, causing a phenomenon known as frequency dispersion, in which transistor current varies depending on the operating frequency. This can result in unstable electrical characteristics and make it difficult to achieve consistent performance. To compensate for these variations, conventional systems have required complex digital correction circuits, increasing overall system size and power losses.
Mitsubishi Electric has addressed this challenge by fabricating GaN transistors using GaN epitaxial layers grown directly on GaN substrates. Using the same semiconductor material for both the substrate and epitaxial layer reduces the crystal defects associated with conventional GaN-on-SiC structures, allowing the transistor to operate closer to its inherent performance capabilities.
As part of a project commissioned by Japan’s Ministry of the Environment, Mitsubishi Electric investigated the relationship between crystal defects and frequency dispersion through detailed device characterization of GaN transistors fabricated on GaN substrates. The researchers developed a new circuit analysis method that incorporates the electrical response associated with crystal defects, enabling them to determine how these defects influence transistor behavior at different operating frequencies.
The results demonstrated that GaN transistors fabricated on GaN substrates exhibit significantly reduced frequency dispersion and flatter frequency characteristics. According to Mitsubishi Electric, this is the first demonstration to clarify the effects of crystal defects on frequency dispersion in GaN transistors using GaN substrates and confirm that these effects can be substantially suppressed.
One of the key benefits of this development is the ability to simplify the digital correction circuits previously required to compensate for frequency-dependent variations. This could reduce RF system complexity, size, and power consumption while improving the consistency of transistor performance.
The technology has potential applications in high-power RF systems, including 5G/6G base stations, radar equipment, and industrial microwave heating systems. By reducing the need for complex correction circuitry, the approach could support the development of more compact and energy-efficient high-frequency equipment.
Mitsubishi Electric plans to build on these findings by further improving the output power and efficiency of GaN transistors, supporting the development of high-performance devices for industrial and communication applications.
Details of the research are being presented at the International Workshop on Nitride Semiconductors 2026 (IWN2026), held from November 8-13 at Kumamoto Castle Hall in Kumamoto City, Japan.