Investigation of bias stress degradation of Depletion-Mode (D-Mode) AlGaN/GaN HEMT

This paper reports the influence of electrical stress on the reliability of AlGaN/GaN HEMTs. Drain step bias stress and gate step bias stress were performed on AlGaN/GaN HEMTs. Several degradation failure modes of DC parameters such as transconductance reduction, threshold voltage positive shifted and gate delay increased were identified. The degradation process of devices characterized by electrical methods. The results show that high drain bias stress is the main reason for electrical stress degradation of devices. Moreover, we have confirmed that the Schottky characteristics of the device are improved after the step bias stress by analyzing variation of the gate to source leakage current and gate to drain leakage current. The gate-source leakage current of device reduced about 50% and the gate to drain leakage current reduced about 35% after the step bias stress. Electrons tunnel through the gate contact barrier into the semiconductor during the high bias electric stress experiments. Electrons were trapped near the gate edge, resulting in partial loss of 2DEG in the transistor channel, thereby accelerating the performance degradation of device. The results may be useful in the application of AlGaN/GaN HEMTs.