Mechanism of Hydrogen-driven Free-electron Generation in Silicon Elucidated for First Time Ever
Will enhance electron-concentration control in silicon power semiconductors to reduce power losses
January 14, 2026
Mitsubishi Electric Corporation
Institute of Science Tokyo
University of Tsukuba
Quemix Corporation
Mitsubishi Electric Corporation, Institute of Science Tokyo, University of Tsukuba, and Quemix Corporation announced today that they have achieved the world’s first1 elucidation of how hydrogen produces free electrons2 through the interaction with certain defects3 in silicon. The achievement has the potential to improve how insulated gate bipolar transistors (IGBTs) are designed and manufactured, making them more efficient and reducing their power loss. It is also expected to open up possibilities for future devices using ultra-wide bandgap (UWBG) materials.4
In the global drive toward carbon neutrality, efforts to make power electronics more efficient and energy-saving are accelerating worldwide. IGBTs are key components responsible for power conversion, so improving their efficiency is a major priority. While hydrogen ion implantation has been used for about half a century to control electron concentration in silicon, the underlying mechanism has remained unclear until now.
In 2023, Mitsubishi Electric and University of Tsukuba jointly discovered a defect complex5 in silicon that contributes to increasing electron concentration. They confirmed that this complex is formed when an interstitial silicon pair and hydrogen bind, but the reason why free electrons are newly generated in this process was still unclear.6 By using advanced computational calculations, the four organizations have now uncovered how hydrogen exists inside the defect complex. They have also explained why hydrogen releases electrons and how these electrons become free within silicon. Furthermore, their findings suggest that this mechanism could also be applied to diamond, a promising material for future power semiconductors that is difficult to control in terms of electron levels.
The full details of this research were published online on January 13 (London time) in Communications Materials, a journal published by Nature Portfolio.
Features
- Mechanism by which a hydrogen-containing defect complex in silicon generates free electrons
For nearly half a century, hydrogen ion implantation into silicon was reported to produce free electrons at locations where hydrogen atoms are present. This technique is now used to form n‑type layers containing free electrons inside power semiconductors such as IGBTs. However, an isolated hydrogen atom in silicon does not necessarily release a free electron,7 so the underlying mechanism remained unclear.
Starting from the hypothesis that hydrogen and crystal defects act together to generate free electrons, joint research by Mitsubishi Electric and University of Tsukuba applied electrical and optical measurements and electron spin resonance (ESR).8 In 2023, this work identified the I4 defect—a structural disturbance formed by extra silicon atoms inserted into the silicon crystal—as being involved in free‑electron generation. To clarify hydrogen’s role, Institute of Science Tokyo and Quemix performed first‑principles calculations9 to models containing hydrogen atoms at multiple candidate sites around the I4 defect to study the resultant structural stability and electronic states10 of defect complexes.
The calculations showed that in defect‑free silicon, a hydrogen atom forms electronic states that do not contribute to free‑electron generation. However, when an I4 defect is nearby, a hydrogen atom can reside in the center positions of bonds11 between silicon atoms. In that configuration, the electronic states associated with the I4 defect shift into a condition that favors electron release. In further analysis based on molecular orbital theory,12 the computational calculation indicates a cooperative effect: an electron associated with a hydrogen atom moves to the I4 defect, and the I4 defect then releases an electron that functions as a free electron. This synergy between defect and hydrogen explains the observed free‑electron generation.
2. Technical demonstration: Up to 20% reduction in power loss in silicon IGBTs and diodes
Mitsubishi Electric has been reducing power loss in silicon IGBTs and diodes by combining hydrogen ion implantation for n‑type layer formation and reducing the thickness of silicon substrates. For example, in a 1,200V-class device, the company has technically demonstrated reductions in total power loss of 10% in IGBTs and 20% in diodes compared with its 7th‑generation products. The fundamental insights gained on hydrogen‑related free‑electron generation, which contributed to the present mechanism elucidation, have supported these power‑loss reductions.
3. Theoretical indication of applicability to UWBG materials
Materials such as diamond and aluminum nitride (AlN) are promising for use in future power semiconductors and quantum sensors, but practical implementation has been hampered by the extreme difficulty of controlling electron concentration via conventional methods. To examine whether the hydrogen‑related free‑electron generation mechanism found in silicon could operate in UWBG materials, initial first‑principles calculations were performed. The results indicate that in diamond—which shares a covalent crystal structure similar to silicon—hydrogen is energetically more stable when incorporated into bonds between carbon atoms rather than occupying interstitial gaps. When paired defects are present, this bond‑center incorporation of hydrogen could enable the same kind of mechanism to function in diamond. This finding suggests a possible route to address electron‑concentration control in certain UWBG materials, at least from a fundamental perspective.
Structural configuration of a hydrogen atom within a diamond crystal
Roles
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Mitsubishi Electric |
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Institute of Science Tokyo |
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University of Tsukuba |
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Quemix |
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This work was supported by Japan Society for the Promotion of Science (JSPS) KAKENHI under Grant-Aid for Scientific Research (nos. 21H04553,20H00340, and 22H01517). Additional support was provided by Center of Innovation for Sustainable Quantum AI (JST, grant number JPMJPF2221).
Future Development
By applying this mechanism to UWBG materials such as diamond, in which electron concentration traditionally has been difficult to control, this approach is aimed at advancing the development of semiconductor devices. These include power semiconductors, high-frequency devices and quantum sensors, all of which are expected to contribute significantly toward the achievement of a carbon-neutral world.
Publication
Title | Advancing N-type doping in semiconductors through hydrogen-defect interactions |
Authors | Akira Kiyoi, Yusuke Nishiya, Yuichiro Matsushita & Takahide Umeda |
Journal | Communications Materials (a journal published by Nature Portfolio) |
Date | January 13, 2026 (London time) |
DOI | 10.1038/s43246-025-00955-4 |
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About Mitsubishi Electric Corporation
With more than 100 years of experience in providing reliable, high-quality products, Mitsubishi Electric Corporation (TOKYO: 6503) is a recognized world leader in the manufacture, marketing and sales of electrical and electronic equipment used in information processing and communications, space development and satellite communications, consumer electronics, industrial technology, energy, transportation and building equipment. Mitsubishi Electric enriches society with technology in the spirit of its “Changes for the Better.” The company recorded a revenue of 5,521.7 billion yen (U.S.$ 36.8 billion*) in the fiscal year ended March 31, 2025. For more information, please visit www.MitsubishiElectric.com
*U.S. dollar amounts are translated from yen at the rate of \150=U.S.$1, the approximate rate on the Tokyo Foreign Exchange Market on March 31, 2025.
About Institute of Science Tokyo
Institute of Science Tokyo (Science Tokyo) was established on October 1, 2024, following the merger between Tokyo Medical and Dental University (TMDU) and Tokyo Institute of Technology (Tokyo Tech), with the mission of “Advancing science and human wellbeing to create value for and with society.”
About University of Tsukuba
University of Tsukuba was established in October 1973, due to the relocation of its antecedent, the Tokyo University of Education, to the Tsukuba area. As the new concept comprehensive university in Japan to be established under a country-wide university reform plan, the University has featured “Openness” with “New Systems for Education and Research” under a “New University Administration.” The university reform plays a major role in our continuing effort for improvement. We are striving to create a unique, active, and internationally competitive university with superlative education and research facilities.
About Quemix Corporation
Quemix Inc., a consolidated subsidiary of TerraSky Co., Ltd. (Headquarters: Chuo-ku, Tokyo; CEO: Hideya Sato), conducts R&D in quantum computers, quantum sensors, and materials computation. Guided by its vision, “Realizing the Future Envisioned through Quantum Technology,” Quemix’s mission is to enable breakthrough innovations for companies leading the quantum era.
Since its establishment in 2019, Quemix has specialized in developing algorithms for Fault-Tolerant Quantum Computers (FTQC). The company developed and patented the Probabilistic Imaginary-Time Evolution (PITE®) algorithm, which has been mathematically proven to achieve quantum speedup in quantum chemistry calculations. As Japan’s pioneer in FTQC algorithms, Quemix aims to bring practical quantum computing applications to materials computation and simulation by 2028.
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