Better electron transport without degrading heat transfer offers a promising path for next-generation power electronic devices.

Power electronic devices help control the flow of electricity and convert it into forms needed by different machines, such as electric vehicles, renewable energy systems, and industrial equipment. Some electrical energy is lost as heat during this process, reducing efficiency and potentially affecting the device’s performance. Semiconductor materials that can withstand high voltages, carry electricity efficiently, and release heat effectively would make these devices more efficient and reliable.

Alpha-gallium oxide (α-Ga₂O₃) is an attractive candidate for this because it can withstand very strong electric fields. However, scientists still do not fully understand how easily electrons move through it or how effectively it releases heat, both of which are important properties for making reliable electronic devices.

To investigate these properties, researchers at Hokkaido University and Kyoto University prepared thin films of alpha-gallium oxide using a technique called mist chemical vapor deposition. They added small amounts of germanium, an element that provides conducting electrons to the material. By varying the amount of germanium, the team could study how changes in electron concentration affect the movement of electricity and heat through the films. The study was published in ACS Applied Electronic Materials.

The team first measured the electrical properties of the films, including electron concentration and thermopower, which describes how many electrons move through a material. Then, the researchers estimated the effective mass of electrons, which describes how electrons behave inside a material. They found that this was approximately 40% of a free electron’s mass, higher than the theoretically predicted value of 25%. This difference could be part of the reason that electrons move less easily through alpha-gallium oxide than expected.

The team then measured how efficiently heat travels through the films. They found a thermal conductivity of approximately 19 watts per meter-kelvin. This value remained almost unchanged even when the germanium concentration increased. Together, these results show that adding germanium can improve electron movement without significantly changing heat transfer through the material. 

By improving our knowledge of how electricity and heat move through alpha-gallium oxide, this research provides a useful foundation for designing future power electronic devices. Further work will be needed to translate this understanding into improved device performance.

Original article:

Hiromichi Ohta, Takeru Wakamatsu, Mitsuki Yoshimura, and Katsuhisa Tanaka. Experimental Determination of Carrier Effective Mass and Cross-plane Thermal Conductivity in Mist-CVD-Grown Ge-Doped α-Ga₂O₃ Epitaxial Films. ACS Applied Electronic Materials. 5 November 2026.

DOI: 10.1021/acsaelm.6c01639

Funding:

This work was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Numbers 26H02188 (Hiromichi Ohta) and 26H02198 (Katsuhisa Tanaka). Mitsuki Yoshimura was supported by a Grant-in-Aid for JSPS Research Fellows (25KJ0452). Part of this work was also supported by the Crossover Alliance to Create the Future with People, Intelligence and Materials, and by the Network Joint Research Center for Materials and Devices.

Contacts:

Professor Hiromichi Ohta
Research Institute for Electronic Science
Hokkaido University
Email: hiromichi.ohta[at]es.hokudai.ac.jp

Megha Kalra
Public Relations & Communications Division
Office of Public Relations and Social Collaboration
Hokkaido University
Email: en-press[at]general.hokudai.ac.jp

Whitney Hubbell
Global Communications
Kyoto University, Clock Tower Ground Floor
Yoshida Honmachi 36-1, Sakyo-ku, Kyoto 606-8501, Japan
Phone +81 (0)75.753.572
Email: hubbell.whitney.4a[at]kyoto-u.ac.jp