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Diamond is a wide bandgap semiconductor and is expected to be applied to power and high-frequency devices due to its high physical properties. In 2016, we reported the first inversion channel diamond MOSFET with normally-off operation and field-effect mobility ( μ FE ) of 8 cm 2 /Vs and then have developed the diamond MOSFET-related technologies. However, the μ FE of the inversion channel diamond MOSFET is 20 cm 2 /Vs, which is still lower than the ideal channel mobility of 3000 cm 2 /Vs. One of the main reasons for the low mobility is the high interface state density ( D it ) of 10 13 cm −2 eV −1 or more generated by the bunching step on the diamond surface. In this study, in order to reduce D it and improve μ FE , we propose the fabrication process of an inversion channel p-type diamond MOSFET with atomically step-free Al 2 O 3 /diamond (111) interface and demonstrate the step-free interface diamond MOSFET. The step-free diamond MOSFET showed normally-off, gate voltage control, and clear saturation characteristics. The μ FE and D it of the step-free diamond MOSFET were 30.6 cm 2 /Vs and 2.8 × 10 12 cm −2 eV −1 , respectively. The D it values are the lowest among the inversion channel diamond MOSFET reported to date for inversion channel MOSFET using an Al 2 O 3 /diamond interface.
Kobayashi et al. (Tue,) studied this question.