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.
Highlights
In recent years, substantial research has been focused on AlGaN/GaN-based high electron mobility transistors (HEMTs) for high-power and radio-frequency applications due to the remarkable properties of III-nitrides such as high saturation velocity (~2 × 107 cm/s), wide band gap (~3.4 eV), high carrier density (~1013 /cm2 ), and large breakdown electric field (>3 MV/cm) [1,2,3]
Ultraviolet/ozone (UV/O3 ) surface plasma treatment is important due to its ability to screen the effects of polarization bound charges of GaN and to produce the Gallium oxide (Ga-O) surface dielectric layer on GaN [12]
Eller et al and Choi et al reported that Gallium oxide (Ga-O) layer is useful as a surface dielectric layer in GaN-based electronic devices [6,13]
Summary
Substantial research has been focused on AlGaN/GaN-based high electron mobility transistors (HEMTs) for high-power and radio-frequency applications due to the remarkable properties of III-nitrides such as high saturation velocity (~2 × 107 cm/s), wide band gap (~3.4 eV), high carrier density (~1013 /cm2 ), and large breakdown electric field (>3 MV/cm) [1,2,3]. Various methods were introduced to improve the surface and interface states, such as wet cleaning [6], dry etching [6], interface passivation layers [7,8], and surface plasma treatment [9,10,11] Among these methods, ultraviolet/ozone (UV/O3 ) surface plasma treatment is important due to its ability to screen the effects of polarization bound charges of GaN and to produce the Ga-O surface dielectric layer on GaN [12]. Eller et al and Choi et al reported that Gallium oxide (Ga-O) layer is useful as a surface dielectric layer in GaN-based electronic devices [6,13]. This method is much easier and simpler to apply than what was previously reported [14]. There are very few available reports that are focused on the improvement of the interface quality of the
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