8 mΩ·cm2vertical GaN-based trench metal–oxide–semiconductor field-effect transistors on a free-standing GaN substrate for 1.2-kV-class operation

In this paper, we report on 1.2-kV-class vertical GaN-based trench metal–oxide–semiconductor field-effect transistors (MOSFETs) on a free-standing GaN substrate with a low specific on-resistance. A redesigned epitaxial layer structure following our previous work with a regular hexagonal trench gate layout enables us to reduce the specific on-resistance to as low as 1.8 mΩ·cm2 while obtaining a sufficient blocking voltage for 1.2-kV-class operation. Normally-off operation with a threshold voltage of 3.5 V is also demonstrated. To the best of our knowledge, this is the first report on vertical GaN-based MOSFETs with a specific on-resistance of less than 2 mΩ·cm2.