Surface potential transient of AlGaN/GaN HEMTs measured by Kelvin probe force microscopy

During the gate bias stress, electrons are injected from the gate to the gate-drain access region and captured by the surface states as shown in Fig. 1. The captured electrons will be emitted when the gate voltage is changed to 0 V. Then, the surface potential is expected to increase gradually in accordance with electron emission. According to the experimental results of the drain recovery after the gate bias stress, the time constant is expected to be several tens seconds [8]. This is sufficiently longer than the response time of the KFM measurement system.