Effects of Surface Oxidation of AlGaN on DC Characteristics of AlGaN/GaN High-Electron-Mobility Transistors

We have investigated the effects of thin native oxide layers on the AlGaN surface on the DC characteristics of AlGaN/GaN high electron mobility transistors (HEMTs). After HEMT fabrication, the AlGaN surface between the electrodes was intentionally oxidized using either O 2 or N 2 O plasma. X-ray photoelectron spectroscopy (XPS) analysis showed that both methods produced a native oxide of AlGaN with a thickness of about 1 nm and that an N–O chemical bond was present in the N 2 O plasma oxide. We observed pronounced degradation in the DC characteristics and current collapse in the HEMT with O 2 plasma oxidation. In contrast, the formation of native oxide by the N 2 O plasma had no effect on the DC characteristics or current stability of the AlGaN/GaN HEMT. Possible mechanisms for device degradation were discussed in terms of stress and deep levels in the AlGaN layer induced by oxide formation or oxygen incorporation.