Gate Technology Contributions to Collapse of Drain Current in AlGaN/GaN Schottky HEMT

Contributions of gate metal to electrical characteristics in AlGaN/GaN Schottky HEMT are reported. The focus is on the collapse of drain current associated with Schottky metals. Ni and W gate introduce electrically active defects under the gate metal in AlGaN layer. These electrically active defects induce the current collapse, higher gate leakage current, and frequency dispersion in C-V characteristics. Contrarily, TiN metal seems to mitigate the appearance of such electrically active defects. The observed current collapse is not the permanent but the recoverable degradation by means of light exposure irrespectively of the gate metals, suggesting the involvement of electron trapping on defects, particularly at the gate edge on the drain side where the electric field is the highest. The nitrogen vacancies in the AlGaN layer underneath the Schottky gate are plausible origin that is responsible for the electrically active defects based on the dependence of nitrogen concentration in TiN metal on the current collapse, which can be explained in terms of nitrogen diffusion from the AlGaN layer to the gate metal.