Ron Increase in GaN HEMTs - Temperature or Trapping Effects

The on-state resistance R-on of GaN devices can be affected by charge trapping as well as temperature effects. For the reliable application of the devices it is useful to distinguish between these two effects and understand the cause of power losses. In this work, three state-of-the-art GaN power transistors are investigated. An obvious R-on increase by trapping occurs in the GaN normally-off devices, whereas the normally-on device has no trapping issues. Trapping mechanisms and the R-on increase with the temperature have similar time constants, which makes it difficult to separate the effects. A feasible approach is to compare a high frequency switching mode to a constant conduction operation that causes the same losses. Furthermore, the contrary dependency of both effects on the duty cycle is used to identify accumulation of trapping. Finally, the increase of the on-state resistance is investigated in a buck converter application.