Comparison of Hydrogen-Induced Oxide Charges Among GaN Metal-Oxide-Semiconductor Capacitors with Al₂O₃, HfO₂, or Hf_0.57Si_0.43O_x Gate Dielectrics

The effect of hydrogen on GaN metal-oxide-semiconductor (MOS) capacitors with Al₂O₃, HfO₂, or Hf_0.57Si_0.43O _x gate dielectrics was studied using capacitance–voltage (C–V) measurements. Hydrogen exposure shifted all the C–V curves toward the negative bias direction, and the hydrogen response of the devices was reversible. When the hydrogen-containing ambient atmosphere was changed to N₂, the C–V characteristics were found to gradually revert to the initial values in N₂. Application of a reverse gate bias accelerated the reversion compared with that in the absence of a bias, indicating that hydrogen was absorbed into the dielectric (Hf_0.57Si_0.43O _x ) as positive mobile charges. This result is consistent with the direction of the shift of the C–V curves; positively charged hydrogen absorbed into a dielectric can cause a flatband voltage shift. The hydrogen-induced shift of the C–V curves varied depending on the dielectric. MOS devices with HfO₂-based high-k dielectrics were found to have approximately two to four times more incorporated charges than devices with Al₂O₃. Under the hypothesis that oxygen vacancies (V_Os) trap hydrogen, the obtained results imply that the number of V_Os in HfO₂-based high-k dielectrics is much larger than that in Al₂O₃-based dielectrics.