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 HEIVIT 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 AIGaN/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. (C) 2009 The Japan Society of Applied Physics