Combined Implications of UV/O₃ Interface Modulation with HfSiO_X Surface Passivation on AlGaN/AlN/GaN MOS-HEMT

Abstract

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/O3) 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 (VTH) of the MOS-HEMT was shifted towards positive due to the band bending at the SiO2/GaN interface by UV/O3 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/O3 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/O3-surface-modified, HfSiOX-passivated MOS-HEMT exhibited a decent performance, with IDMAX of 655 mA/mm, GMMAX of 116 mS/mm, higher ION/IOFF ratio of approximately 107, and subthreshold swing of 85 mV/dec with significantly reduced gate leakage current (IG) of 9.1 ×10−10 A/mm.

Keywords

• AlGaN/AlN/GaN
• gallium oxide
• MOS-HEMT
• HfSiO_X
• UV/O₃
• passivation