Investigation of the dynamic on-state resistance of 600V normally-off and normally-on GaN HEMTs

In this paper, current collapse phenomena and thermal effects in newly developed normally-off and normally-on GaN HEMTs are investigated. The experimental results show that a high off-state voltage and high switched drain current at high junction temperature cause an increase of the on-state resistance. During switching from 50 kHz to 400 kHz, an increase of R_DSON is observed for both types of GaN devices. It is evident that the number of switching transients significantly influences the increase of the on-state resistance, suggesting that this increase is due to a current collapse in GaN HEMTs. A detailed comparison of the evaluated R_DSON between GaN transistors and the newest high-speed CoolMOS-C7 transistor is presented.