【International Papers】Hydrogen passivation of electron traps and fixed charges in SiO₂/β-Ga₂O₃(001) MOS structures

      Researchers from the The University of Osaka have published a dissertation titled "Hydrogen passivation of electron traps and fixed charges in SiO₂/β-Ga₂O₃(001) MOS structures  " in Applied Physics Letters.

Background

      β-Gallium oxide (β-Ga₂O₃) has a wide bandgap (4.9 eV) and a high breakdown electric field (8 MV/cm), making it a promising candidate for next-generation power semiconductor materials. The growth processes of β-Ga₂O₃ bulk crystals, such as the edge-defined film-fed growth method and the Czochralski method, do not require high pressure, resulting in lower manufacturing costs compared with other widegap semiconductors. Single-crystalline β-Ga₂O₃ epitaxial layers can be grown by hydride vapor phase epitaxy, and the donor concentration can be controlled over a wide range: 10¹⁵–10¹⁹ cm⁻³. Despite these advantages, Ga₂O₃ suffers from low thermal conductivity and challenges in achieving p-type conduction. The former problem can be compensated by placing Ga₂O₃ on top of high-thermal-conductivity materials such as silicon carbide. As for the latter, a solution is to use a semi-insulating region instead of p-type region in the device structure. A variety of power devices, including vertical Schottky barrier diodes, depletion-mode metal-oxide-semiconductor field-effect transistors (MOSFETs), and superjunction-equivalent MOSFETs, have been reported so far, highlighting the growing interest in Ga₂O₃.

      In the present study, we investigated the impact of post-metallization forming gas annealing (FG-PMA) on the interface and dielectric properties of SiO₂/β-Ga₂O₃ MOS structures. In the case of Si MOS structures, FG annealing is known to introduce hydrogen atoms that efficiently terminate the silicon dangling bonds (P_b center) at the SiO₂/Si interface. Hydrogen atoms are also effective in passivating the carbon-dangling bonds (P_bC center) at the SiO₂/SiC interface. Unlike these covalent semiconductors, Ga₂O₃ has an ionic bonding character, but it is still meaningful to examine the impact of FG-PMA, which is widely used in semiconductor technology.

Abstract

      We investigated the effect of post-metallization forming gas annealing (FG-PMA) on SiO₂/β-gallium oxide [β-Ga₂O₃(001)] MOS structures. We found that FG-PMA at a relatively low temperature (200–400 °C) efficiently reduced the interface and near-interface defects, resulting in improvements to device performance and reliability. By performing FG-PMA after post-deposition annealing in O₂ and N₂ atmospheres, the interface state density near the conduction band edge of Ga₂O₃ was reduced to as low as (4–7) × 10¹⁰ eV⁻¹ cm⁻². The significant improvement in electrical properties was attributed to the passivation of electrical defects by hydrogen atoms.

Conclusion

      In summary, the investigation of the effect of FG-PMA on SiO₂/β-Ga₂O₃(001) MOS structures confirmed that FG-PMA at a relatively low temperature (200–400 °C) reduced interface defects, fixed charges, and near-interface oxide traps. By performing FG-PMA after combined O₂ and N₂ annealing, the interface state density near the conduction band edge of Ga₂O₃ was reduced to as low as (4–7) × 10¹⁰ eV⁻¹ cm⁻². These improvements in electrical properties are attributed to passivation of defects by hydrogen atoms.