Investigation on the Degradation Mechanism for GaN Cascode Device Under Repetitive Hard-Switching Stress

The degradations of electrical parameters for depletion mode GaN devices in the cascode configuration under repetitive hard-switching stress are investigated in detail. With the help of TCAD simulations and comprehensive experimental analysis, two different mechanisms behind the degradations are demonstrated. Under a relatively low V ds hard-switching condition, hot electron injection is proved to be the only influence factor, which results in the increase of R dson under low gate bias voltage. Furthermore, under the low V ds switching condition, influence of different stages on the degradation trend of the device is verified. It is found that the turn- on procedure has a greater degradation risk due to higher energy consumption. However, when V ds is high during hard-switching, the surface trapping effect is triggered due to high electric field at the end of gate field plate, and finally leads to the device degradation trend. It results in the increase of the R dson under high gate bias condition. Therefore, considering the stability and safety of power systems, which adopt cascode devices as switches, shorter turn- on time or a soft-switching operation condition should be considered in the design.