Degradation Mechanism of Normally-On AlGaN/GaN HEMTs Under Short- and Long-Term HTRB Stress

In this article, the degradations of normally-ON AlGaN/GaN high electron mobility transistors (HEMTs) induced by the short-term and long-term high-temperature reverse bias (HTRB) stress have been investigated systematically. HTRB stress in situ tests was applied to samples in high temperature by changing stress time. In short-term stress, threshold voltage drifted positively sharply and then constantly drifted negatively with gate leakage decreasing. In long-term stress, the threshold voltage started positively drifting after fluctuation. Further research showed that there were three mechanisms dominated changes in device performance, which were distinguished by the stress time. The acceptor type traps present in GaN buffer layer, AlGaN barrier layer, and semiconductor surface ionized result in net negative charge density increased at the beginning of the stress, while with increasing stress time, the dielectric layer under the gate consumed and the interfacial state density decreased. As time continues to increase, the increase of trap density as well as the change of tunneling mechanism affect the characteristics of the device finally. These mechanisms can provide some guidance for the design of GaN microwave devices.