GaAs/H₂O₂ electrochemical interface studied in situ by infrared spectroscopy and ultraviolet-visible ellipsometry part I: Identification of chemical species

Chemical species at the electrochemical interface between n-GaAs(100) and H₂C₂ in 0.5 M H₂SO₄ are identified by in situ infrared spectroscopy and in situ ultraviolet-visible ellipsometry. Under anodic conditions, H₂O₂ dissolves GaAs chemically, and the surface appears rough but clean of other phases. The sulfate concentration near the surface increases to compensate for the charge of the Ga³⁺ ions produced by dissolution. Under cathodic conditions, H₂O₂ is reduced electrochemically, but chemical GaAs dissolution is never completely suppressed; both dissolution products are indirectly detected, the Ga³⁺ ions because they lead to an increase in the local sulfate concentration and HAsO₂ because part of it is reduced cathodically, giving islands of a solid arsenic hydride, most likely As₂H₂. Variations in the amount of As₂H₂ and its surface coverage by adsorbed H and OH groups affect the H₂O₂ reduction rate. A kinetic model is proposed for the interfacial chemistry and electrochemistry. Numerical simulations reproduce the main features of experimental currentpotential scans, including the presence of a negative slope region related to oscillatory behavior.