Investigation of the role of pre-existing oxide in the initial degradation mechanism in AlGaN/GaN HEMTs under ON-state stress

The role of pre-existing oxide in the initial degradation mechanism of AlGaN/GaN high electron mobility transistors during ON-state stressing was systematically studied. The pre-existing oxide was revealed to exist as an amorphous oxide layer consisting primarily of Ni and Ga oxides with a small amount of Al oxide at the GaN-cap/Ni-gate interface. Through an ON-state stressing experiment carried out in vacuum that excluded the influence of atmospheric oxygen, we discovered that the pre-existing interfacial oxide participated in an electrochemical reaction, accounting for the initial degradation in AlGaN/GaN HEMTs. The thickening of the oxide layer at the gate edge reduces the effective gate length of the device, thereby causing a decrease in the drain saturation current.