Impact of Water-Assisted Electrochemical Reactions on the OFF-State Degradation of AlGaN/GaN HEMTs

The origin of structural and electrical degradation in AlGaN/GaN high-electron mobility transistors (HEMTs) under OFF-state stress was systematically studied. Hydroxyl groups (OH-) from the environment and/or adsorbed water on the III-N surface, were found to play an important role in the formation of surface pits during OFF-state electrical stress. The mechanism of this water-related structural degradation is explained by an electrochemical cell formed at the gate edge where gate metal, the III-N surface, and the passivation layer meet. The relationship between structural and electrical degradation in AlGaN/GaN HEMTs under OFF-state stress is discussed. Specifically, the permanent decrease in the drain current is directly linked with the formation of the surface pits, while the permanent increase in the gate current is found to be uncorrelated with the structural degradation.