Study of an Al₂O₃/GaN Interface for Normally Off MOS-Channel High-Electron-Mobility Transistors Using XPS Characterization: The Impact of Wet Surface Treatment on Threshold Voltage V_TH

Understanding the impact of GaN surface treatment conditions on dielectric/GaN interface chemical properties is critically important for device performance. This point is under intensive research for the dielectric/GaN structure because GaN does not have a good native oxide quality such as SiO2 used in silicon technologies. The effects of different wet treatments prior to atomic layer deposition (ALD) of thin Al2O3 on Ga-polar GaN were studied by X-ray photoelectron spectroscopy (XPS). The same wet treatments have been applied to the recessed region of AlGaN/GaN heterostructures, followed by ALD of 30 nm Al2O3 in order to form MOS-channel high-electron-mobility transistors (MOSc-HEMTs) on 200 mm GaN-on-Si wafers with CMOS compatible processing. The resulting transistors exhibited a normally off behavior (threshold voltage VTH = 0.4–0.6 V) and their VTH was correlated to the oxidation at the Al2O3/GaN interface, suggesting the presence of donor defects.