Associate Professor Yuichiro Matsushita of Materials and Structures Laboratory, Institute of Science Tokyo, Mitsubishi Electric Corporation, Associate Professor Takahide Umeda of Institute of Pure and Applied Sciences, University of Tsukuba and Quemix Corporation announced 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
1) 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.
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.
1 According to research conducted by Mitsubishi Electric as of January 14, 2026.
2 Electrons that can move freely within a silicon crystal. Their concentration is controlled by the intentional introduction of specific Impurities.
3 Structural imperfections that affect the mobility and recombination of free electrons.
4 Diamond, aluminum nitride, etc. semiconductors with a larger bandgap than conventional silicon or silicon carbide semiconductors.
5 A defect complex composed of intrinsic defects—such as silicon interstitials—and extrinsic defects, like hydrogen. In power semiconductors, such defect complexes are intentionally created to control device performance.
6 "How does hydrogen transform into shallow donors in silicon?", Phys. Rev. B 108, 235201 (2023).
7 In a defect-free silicon, hydrogen atoms settle into positions known as tetrahedral sites or bond-centered sites, depending on their charge states where they form an electronic state that cannot generate free electrons.
8 A spectroscopy technique used to detect unpaired electrons in a magnetic field.
9 A computational method that predicts the material properties based on the laws of quantum mechanics, without relying on experimental data.
10 The energy level of an electronic state is important to control electron concentration, because if thermal energy exceeds this level, electrons can be thermally excited and become available as free electrons.
11 Bonds within a crystal are the forces that make atoms or molecules keep specific crystal structure, influencing the material's physical properties such as hardness, electrical conductivity and melting point.
12 A theory used to understand the arrangement and energy states of electrons within a molecule.
13 A quantum mechanics-based computational method that treats electron density as a fundamental variable and calculates electronic states to predict the properties of materials.
