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

Abstract

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 O2 or N2O 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 N2O plasma oxide. We observed pronounced degradation in the DC characteristics and current collapse in the HEMT with O2 plasma oxidation. In contrast, the formation of native oxide by the N2O 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.