High-speed switching and current-collapse-free operation by GaN gate injection transistors with thick GaN buffer on bulk GaN substrates

GaN-based normally-off Gate Injection Transistors (GITs) with p-type gate over AlGaN/GaN heterojunction are fabricated on bulk GaN substrates. Thickness of insulating GaN buffer layer is increased up to 16 μm for the presented device from 5 μm for conventional GITs on Si. The thick buffer reduces the parasitic output capacitances, which enables fast turn-off switching. The thick buffer and the use of bulk GaN substrate help to improve the crystal quality of AlGaN/GaN so that the sheet resistance is reduced. Improved crystal quality together with reduced trap density successfully suppresses the current collapse up to 1 kV or higher of the applied drain voltage. The resultant R
_on
Q
_oss
(R
_on
: on-state resistance, Q
_oss
: output charge) as a figure-of-merit for high speed turn-off switching is reduced down to 940 mΩnC that is one third from that of GITs on Si. The resultant turn-off dV
_ds
/dt reaches as large as 285 V/ns that is twice higher than reported values by GITs on Si.