Surface passivation is critically important to improve the current collapse and the overall device performance in metal-oxide semiconductor high-electron mobility transistors (MOS-HEMTs) and, thus, their reliability. In this paper, we demonstrate the surface passivation effects in AlGaN/AlN/GaN-based MOS-HEMTs using ultraviolet-ozone (UV/O-3) plasma treatment prior to SiO2 -gate dielectric deposition. X-ray photoelectron spectroscopy (XPS) was used to verify the improved passivation of the GaN surface. The threshold voltage (V-TH) of the MOS-HEMT was shifted towards positive due to the band bending at the SiO2/GaN interface by UV/O-3 surface treatment. In addition, the device performance, especially the current collapse, hysteresis, and 1/f characteristics, was further significantly improved with an additional 15 nm thick hafnium silicate (HfSiOX) passivation layer after the gate metallization. Due to combined effects of the UV/O-3 plasma treatment and HfSiOX surface passivation, the magnitude of the interface trap density was effectively reduced, which further improved the current collapse significantly in SiO2-MOS-HEMT to 0.6% from 10%. The UV/O-3-surface-modified, HfSiOX-passivated MOS-HEMT exhibited a decent performance, with I-DMAX of 655 mA/mm, G(MMAX) of 116 mS/mm, higher I-ON/I-OFF ratio of approximately 107, and subthreshold swing of 85 mV/dec with significantly reduced gate leakage current (I-G) of 9.1 x 10(-10) A/mm.
