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This paper reports an extensive analysis of the physical mechanisms responsible for the failure of GaN-based metal-insulator-semiconductor (MIS) high electron mobility transistors (HEMTs). When stressed under high applied electric fields, the traps at the dielectric/III-N barrier interface and inside the III-N barrier cause an increase in dynamic on-resistance and a shift of threshold voltage, which might affect the long term stability of these devices. More detailed investigations are needed to identify epitaxy-or process-related degradation mechanisms and to understand their impact on electrical properties. The present paper proposes a suitable methodology to characterize the degradation and failure mechanisms of GaN MIS-HEMTs subjected to stress under various off-state conditions. There are three major stress conditions that include: V DS = 0 V, off, and off (cascode-connection) states. Changes of direct current (DC) figures of merit in voltage step-stress experiments are measured, statistics are studied, and correlations are investigated. Hot electron stress produces permanent change which can be attributed to charge trapping phenomena and the generation of deep levels or interface states. The simultaneous generation of interface (and/or bulk) and buffer traps can account for the observed degradation modes and mechanisms. These findings provide several critical characteristics to evaluate the electrical reliability of GaN MIS-HEMTs which are borne out by step-stress experiments.

This study comprehensively analyzed the reliability of trapping and hot-electron effects responsible for the dynamic on-resistance (Ron) of GaN-based metal-insulator-semiconductor high electron mobility transistors. Specifically, this study performed the following analyses. First, we developed the on-the-fly Ron measurement to analyze the effects of traps during stress. With this technique, the faster one (with a pulse period of 20 ms) can characterize the degradation; the transient behavior could be monitored accurately by such short measurement pulse. Then, dynamic Ron transients were investigated under different bias conditions, including combined off state stress conditions, back-gating stress conditions, and semi-on stress conditions, in separate investigations of surface-and buffer-, and hot-electron-related trapping effects. Finally, the experiments showed that the Ron increase in semi-on state is significantly correlated with the high drain voltage and relatively high current levels (compared with the offstate current), involving the injection of greater amount of hot electrons from the channel into the AlGaN/insulator interface and the GaN buffer. These findings provide a path for device engineering to clarify the possible origins for electron traps and to accelerate the development of emerging GaN technologies.

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