Dynamic Extension Behavior of the Depletion Region in GaN HEMTs Monitored with a Channel-Probe Branch Structure

This letter proposes a method to monitor the dynamic extension process of the depletion region in GaN HEMTs. Based on a channel-probe branch structure, the transient channel potential (V_CP) at a certain distance from the gate was measured under off-state conditions. From the transient V_CP curves, the extension time of the depletion region was directly obtained for the first time, and it was found to exhibit an exponential dependence on the drain-gate bias (V_DG) under off-state conditions. Comparison study of devices with and without SiN_x passivation reveals the dominant role of surface traps in the extension process. The equivalent surface charging current is derived from the extension time of the depletion region, with which the dominated surface charge transport mechanism is revealed to be Poole-Frenkel emission.