Vertical GaN-based power devices on bulk GaN substrates for future power switching systems

We propose a normally-off vertical GaN-based transistor on a bulk GaN substrate with low specific on-state resistance of 1.0 mΩ·cm² and high off-state breakdown voltage of 1.7 kV. P-GaN/AlGaN/GaN triple layers are epitaxially regrown over V-shaped grooves formed over the drift layer. The channel utilizes so-called semi-polar face with reduced sheet carrier concentration at the AlGaN/GaN interface, which enables high threshold voltage of 2.5 V and stable switching operations. The employed p-type gate does not give any concern of the gate instability. Note that formation of carbon doped insulating GaN layer formed on p-GaN well layer underneath the channel suppresses the punch-through current at off-state between the source and drain, which enables good off-state characteristics. The fabricated high-current vertical transistor achieves successful fast switching at 400V/15A. We also propose a novel vertical GaN-based junction barrier Schottky (JBS) diode with trenched p-GaN region on a bulk GaN substrate. A specific differential on-resistance of the GaN JBS diode is 0.9 mΩ·cm² while keeping high breakdown voltage of 1.6 kV. These results indicate that the demonstrated vertical GaN devices are very promising for future high power switching applications.