Effect of Substrate Bias in Ohmic p-Gate GaN-HEMTs on Unclamped Inductive Switching Capability

The unclamped inductive switching (UIS) capabilities of ohmic p-gate gallium nitride (GaN)-high electron mobility transistor (HEMT) under various substrate bias conditions were measured. One of the critical disadvantages of GaN-HEMTs is their ultralow UIS capability because there is no structure for the removal of holes generated by the impact ionization. Therefore, the failure position due to overvoltage stress strongly depends on the current path of the holes generated by impact ionization. This article reports that the UIS capability of ohmic p-gate GaN-HEMTs can be improved by a floating or positive biased substrate condition due to the modulation of the hole current path. Additionally, increasing the gate resistance in the floating substrate condition slows down dV/dt, leading to a greater amount of energy being consumed in the semi-on state, which in turn increases the UIS capability.