Thermal instability during short circuit of normally-off AlGaN/GaN HFETs

•We investigated the short circuit behaviour of GaN HFET devices.•We demonstrated that an unstable phenomenon takes place.•We demonstrate that the threshold voltage begins to decrease at high temperature.•We hypothesize that the observed instability is related to the gate voltage decrease.

The short circuit behaviour of commercial 200 V AlGaN/GaN HFET devices is investigated, clearly evidencing a poor sustainability of such condition. It is observed that, during overcurrent, the drain current tends to increase, exhibiting unstable behaviour. A confirmation of such instability is given by the gate leakage, which also diverges during critical commutations. Measurements evidence a decrease in the threshold voltage at very high temperatures, which is a possible interpretation of the phenomenon.Some waveforms showing a rupture at 50% of the nominal voltage have been reported, evidencing thermal breakdown in about 2 μs.