Inversion-channel MOSFETs on heteroepitaxially grown free-standing diamond using Si-based substrates

Kanazawa, Japan – The MOSFET—metal-oxide-semiconductor field-effect transistor—might not be familiar to most people, but the electronic devices many of us have come to rely on would not be available without these power-switching devices. Making sure sophisticated developments in MOSFET technology can be made commercially viable is the challenge that rapidly follows any exciting steps forward in this area. Researchers at Kanazawa University have demonstrated a substrate preparation method that could open up the latest advances to consumers. Their findings are published in Carbon.

The aesthetic qualities of diamond are well known and appreciated by many, but diamond also has an important practical side. Its excellent thermal and electronic properties make it an attractive material for use in MOSFETs. Diamond MOSFETs are the subject of continual research and improvement. For example, in 2016 the researchers were the first to develop inversion-type p-channel homoepitaxial diamond MOSFETs that have what is described as “normally off” characteristics. This “normally off” state makes the MOSFETs easier and more potential to tune for their intended applications.

However, the homoepitaxial growth techniques used to prepare the inversion-type p-channel diamond MOSFETs limited their production due to the substrate size limitation. Now, Kanazawa University researchers have proposed a method of growing diamond on a silicon-based substrate that will significantly reduce the cost of diamond MOSFETs and accelerate their commercialization.

“One way of making diamond MOSFETs more cost effective is to use a diamond layer that is grown on a layer of silicon-based material,” Group leader-Prof. Norio Tokuda said, “Silicon can be obtained in large wafers and is relatively cheap, so it is an attractive substrate to use. This approach is known as heteroepitaxial growth because a different crystal layer is grown on top of an existing crystal substrate.”

Some devices based on heteroepitaxial diamond substrates have been reported; however, this is the first time to use heteroepitaxially-grown diamond to fabricate inversion-type diamond MOSFETs.

The electronic properties of the heteroepitaxial diamond MOSFETs were tested, and although the characteristics did not all parallel those of homoepitaxially grown diamond devices, the findings provided a positive first step towards widespread application.

“We took a close look at the surfaces of our new devices and found that they are somewhat rougher than their homoepitaxially grown counterparts,” Prof. Norio Tokuda explains, “We believe this explains their comparably lower performance; however, it provides us with a clear focus for future improvements. We are confident that heteroepitaxially grown diamond will be key to optimizing MOSFETs for the commercial market.”


Title: Inversion channel MOSFET on heteroepitaxially grown free-standing diamond


Authors:Xufang Zhang, Tsubasa Matsumoto, Yuta Nakano, Hitoshi Noguchi, Hiromitsu Kato, Toshiharu Makino, Daisuke Takeuchi, Masahiko Ogura, Satoshi Yamasaki, Christoph E. Nebel, Takao Inokuma, Norio Tokuda

DOI: 10.1016/j.carbon.2020.11.072


This work was partially supported by NEDO Feasibility Study Program (Uncharted Territory Challenge 2050) grant number 19101600e0, Kanazawa University SAKIGAKE Project 2018 and 2020, JSPS KAKENHI grant numbers JP17H02786, JP18KK0383, JP19K15042, JP20K14773.

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