IN Brief:
- Mitsubishi Electric has demonstrated suppressed frequency dispersion in high-frequency GaN transistors fabricated on GaN substrates.
- Its circuit analysis method incorporates the response of crystal defects to explain variations in transistor current at different frequencies.
- The research could reduce some digital correction requirements, but commercial qualification and quantified system-level energy savings remain unreported.
Mitsubishi Electric has demonstrated suppressed frequency dispersion in high-frequency gallium nitride transistors fabricated on GaN substrates, using a new analysis method to investigate the relationship between semiconductor crystal defects and electrical behaviour.
The Japanese manufacturer found that devices incorporating GaN epitaxial layers grown on GaN substrates exhibited comparatively flat frequency characteristics. The results indicate a possible route to more consistent transistor operation and reduced requirements for digital correction circuitry in microwave and radiofrequency equipment.
The development addresses frequency dispersion, a phenomenon in which the electrical characteristics of a device vary according to the frequency or timescale of its operating signals. In the transistor structures investigated by Mitsubishi Electric, crystal defects were associated with changes in current response during high-frequency operation.
Gallium nitride is used in high-power radiofrequency devices because its semiconductor properties support substantial electric fields and operation at high frequencies. These characteristics are valuable in equipment such as microwave power systems, communications transmitters, and radar electronics.
Manufacturing the active GaN layers involves growing crystalline material on a suitable substrate. Conventional high-frequency GaN transistors commonly use silicon carbide substrates, whose thermal conductivity assists with removing heat generated during operation.
However, GaN and silicon carbide are different materials, and the formation of an epitaxial layer on a dissimilar substrate can introduce defects associated with the growth process. Such defects can affect the distribution and movement of charge within the completed semiconductor structure.
Some defects interact with charge carriers in ways that depend on the applied electrical conditions. Their response may differ between measurement frequencies, producing variations in current that complicate the relationship between the input signal and the transistor's output.
In a radiofrequency amplifier, this behaviour can make it more difficult to maintain consistent electrical characteristics across the required operating range. The surrounding electronics may need additional compensation to correct variations that would otherwise affect the intended signal response.
Digital correction circuits can provide part of that compensation, but they introduce computational and electrical requirements of their own. Depending on the application, correction functions may increase the complexity, physical size, and power consumption of the complete system.
Mitsubishi Electric investigated whether reducing defect-related effects within the semiconductor structure could lessen the need for such correction. Its experimental devices used GaN substrates beneath the GaN epitaxial material, providing a more closely matched crystalline foundation than conventional GaN-on-SiC structures.
The researchers also developed a circuit analysis method that incorporates the electrical response associated with crystal defects. This allowed the measured frequency dispersion to be examined in relation to defect behaviour rather than treated solely as an unexplained variation in the transistor's external characteristics.
By combining the analysis with experimental device characterisation, Mitsubishi Electric demonstrated a substantial suppression of frequency dispersion in its GaN-on-GaN transistors. The company reports that the resulting characteristics remained comparatively flat across the conditions examined.
The manufacturer describes the achievement as a world-first demonstration, based on its review of 156 research papers in October 2026. That claim concerns the particular analysis and suppression of frequency dispersion demonstrated in the research; it does not mean that the company has fabricated the first GaN transistor using a GaN substrate.
The initial technical disclosure does not provide a complete numerical comparison of dispersion before and after the change, or a detailed set of measured amplifier efficiency improvements. The reported result therefore establishes an experimental advance without quantifying the benefit that would be obtained in a finished commercial transmitter.
Reducing dispersion at device level could simplify subsequent circuit design, although the electrical characteristics of a complete amplifier depend on more than the substrate. Device geometry, bias conditions, matching networks, packaging, and temperature can all influence operation.
Thermal behaviour is another important consideration. Silicon carbide remains attractive as a substrate because of its ability to conduct heat away from high-power devices. Changing to GaN substrates introduces different material and heat-transfer characteristics that must be considered when developing a production transistor.
Substrate economics also influence semiconductor manufacturing decisions. The availability, diameter, defect density, and cost of GaN wafers differ from those of established silicon carbide substrates, making commercial adoption dependent on the relationship between electrical performance and manufacturing cost.
Mitsubishi Electric identifies industrial microwave heating as one potential application. In such equipment, power transistors generate high-frequency electrical energy that can be coupled into a process requiring controlled microwave heating.
The company is investigating the technology within a Japanese Ministry of the Environment programme concerned with components and materials that could contribute to reducing carbon dioxide emissions. One identified application involves chemical recycling systems that use microwave heating during the conversion of waste plastics into chemical feedstocks.
GaN radiofrequency devices are also relevant to mobile communications infrastructure and radar equipment. These applications require power amplification with defined frequency, efficiency, and signal-quality characteristics, while the electrical and thermal operating conditions influence how the semiconductor must be controlled.
Lower device-level frequency dispersion may reduce the correction required for particular operating conditions, but the amount of circuitry that could be removed depends on the amplifier architecture and its performance requirements. Other compensation functions may remain necessary even when dispersion associated with crystal defects is reduced.
The work has been conducted as part of the Ministry of the Environment programme in which Mitsubishi Electric has participated since 2024. Further details are being presented at the International Workshop on Nitride Semiconductors 2026 in Kumamoto, Japan, from 8 to 13 November.
Mitsubishi Electric has not announced a commercial device based on the research or a manufacturing qualification timetable. Further development will need to establish device reliability, repeatable fabrication characteristics, thermal performance, and the extent to which the experimental improvement reduces correction requirements in complete radiofrequency systems.
