[Researcher Information]

• Yi Shuang, Assistant Professor, Department of Materials Solutions, Graduate School of Engineering, Tohoku University. web

[Key Points]

• By utilizing residual oxygen within a sputtering (Note 1) system as a controllable factor rather than an impurity to be removed, the team achieved a conduction type conversion (Note 2) from n-type to p-type in chromium nitride (CrN) thin films without any intentional elemental doping.
• The study elucidated that oxygen acts as a key factor in controlling defects within the crystal structure.
• The successful fabrication of both n-type and p-type CrN thin films using a single material with the same crystal structure paves the way for high-heat-resistance n-p homojunction (Note 3) thin-film thermoelectric devices.

[Abstract]

In recent years, interest has grown in thin-film thermoelectric materials (Note 4) suitable for integration and miniaturization. Among these, transition metal nitrides are considered promising due to their stable operation in high-temperature environments. In particular, chromium nitride (CrN) is known for its excellent n-type thermoelectric properties. However, practical thin-film thermoelectric modules require both n-type and p-type versions of the same material system, and conventional methods have faced challenges due to process complexity.

A research group led by Assistant Professor Yi Shuang and Professor Yuji Sutou at the Tohoku University Graduate School of Engineering has discovered that the conduction type of CrN thin films can be converted from n-type to p-type by controlling the reactive nitrogen gas flow rate while utilizing residual oxygen in the sputtering system. At low flow rates, the films exhibit n-type conductivity due to nitrogen vacancies, whereas increasing the flow rate stabilizes chromium vacancies, shifting the conductivity to p-type. Synchrotron radiation experiments and first-principles calculations revealed that oxygen functions as a factor controlling defect formation.

These results provide a new material control guideline that enables both n-type and p-type conductivity in a single material without intentional doping. This represents a significant step toward the realization of nitride thin-film thermoelectric devices with superior heat resistance.

The results of this study were published in the Royal Society of Chemistry journal Journal of Materials Chemistry A on March 6, 2026.

For more details, please click here.

※Professor Yuta Saito of the Research Center for Green X-Tech (Green Goals Initiative, Tohoku University) is also a collaborator on this research, and this press release is also issued by the center.