Wet oxidation of AlGaAs: The role of hydrogen

Wet oxidation of AlGaAs to form Al₂O₃ by the reduction of H⁺ from water to H produces intermediate As₂O₃. Reduction of As₂O₃ by H to elemental As enables the escape of arsenic from the oxidized film. Further reduction of As to AsH₃ can provide another volatile As species. Formation of intermediate As is problematic for the use of wet oxidation in metal-insulator-semiconductor applications. The kinetic balance between As₂O₃ formation and As escape can explain the transition between the linear and parabolic time dependence of the wet oxidation of buried AlGaAs layers. The near-total suppression of wet oxidation by O₂ is attributed to the suppression of volatile product formation through consumption of atomic hydrogen by reaction with O₂ to form H₂O in preference to the hydrogen reduction of As₂O₃.