Schottky gate of AlGaN/GaN HEMTs: investigation with DC and low frequency noise measurements after 7000 hours HTOL test

This paper reports on AlGaN/GaN high electron mobility transistors (HEMTs) that have been aged by high temperature operating life test (HTOL) during 7000 hours. DC characterization of some aged devices revealed an electrical parasitic effect named "Belly-Shape" that is detected on the gatesource and gate-drain diodes forward current-voltage characteristics. The belly-shape effect is characterized by higher gate current compared to the one of the virgin device for VGS/D below 1.2V. Low frequency gate current noise measurements have been performed at 300K and V-DS=0V to analyze the physical origin of this parasitic effect. The relative LF gate current noise is higher for aged than for virgin devices. For V-GS/D < 1.2V, devices without the parasitic effect exhibit 1/f(gamma) noise which is proportional to the square of IG, while the devices with the parasitic effect exhibit visible Lorentzian noise that is that is nonrepeatable even when measured with the same bias conditions as well as the belly shape effect in the dc characteristics. On the contrary, all devices present 1/f(gamma) noise for V-GS/D > 1.2V where the gate current is governed by diode series resistance.