Direct Observation of Gate Leakage Paths in AlGaN/GaN High Electron Mobility Transistors by Electron Beam–Induced Current

In this study, the electron beam-induced current technique was used to investigate the spatial distribution of gate leakage paths in AlGaN/GaN high electron mobility transistors. The mesa-type devices exhibited three leakage paths: the mesa edge leakage, the sidewall leakage, and the isolation leakage. In mesa-isolated devices with a SiN passivation layer, the dominant leakage paths were through the SiN/GaN interface as a result of the imperfections at the SiN/semiconductor interface. The mesa sidewall leakage in a passivated device gradually decreased from the gate to the source/drain along the mesa edge. This was correlated with the diffusion length and the distance of the electron beam from the gate. In the device without a SiN passivation layer, the major leakage path was found to be through the mesa edge under the gate metal, which was induced by the gate-channel overlap at the mesa edge.