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.

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This paper reports the characteristics of vertical GaN-based trench metal-oxide-semiconductor field-effect transistors on a free-standing GaN substrate with a blocking voltage of 1.6 kV. The high blocking voltage was obtained by using field plate edge termination around the isolation mesa of the transistor. To our knowledge, the blocking voltage is the highest ever reported for vertical GaN-based transistors on free-standing GaN substrates. Normally off operation with a threshold voltage of 7 V is also demonstrated.

Gallium nitride (GaN) is an attractive material for high-frequency and high-power devices. Due to the availability of relatively high-quality free-standing bulk GaN substrates, the research and development of vertical GaN devices on GaN substrates has made significant progress in recent years, and various transistors and diodes based on vertical GaN with excellent characteristics have been reported. This paper reviews the current status and recent progress of vertical GaN power device development reported from companies and research institutions, which includes the technological development of our recent research results of Schottky barrier diodes and trench MOSFETs. Key remaining issues for practical applications are also described.

This paper reports on vertical GaN Schottky barrier diodes (SBDs) fabricated on a free-standing GaN substrate with different sizes of Schottky electrode. The fabricated SBDs with 3 × 3 mm2 Schottky electrodes exhibited both a forward current of 50 A and a blocking voltage of 790 V. To our knowledge, the characteristics of operation with a simultaneous high forward current and high blocking voltage are reported for the first time for vertical GaN SBDs on free-standing GaN substrates. The dependence of these characteristics on the Schottky electrode size is also reported in detail.