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.