Localization and analysis of surface charges trapped in AlGaN/GaN HEMTs using multiple secondary MIS gates

Using an experimental AlGaN/GaN HEMT with a primary Schottky gate and three secondary MIS gates the charge trapping in the passivation layer and at the AlGaN/passivation interface layer is analyzed. The primary device is subjected to off-state drain-source voltage stress. This is followed by electrical characterization using the individual secondary gates, which allows for profiling the spatial distribution of trapped charges below the secondary gates and indicates less pronounced charge trapping towards the drain of the transistor. Experimental findings are verified by TCAD simulations. A physical equivalent network of the carrier injection and surface related trapping is proposed and experimentally verified. These novel results can be exploited for optimum field plate designs and improved compact models of HEMTs.