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 H 2O2 in 0.5 M H2SO4 are identified by in situ infrared spectroscopy and in s itu ultraviolet-visible ellipsometry. Under anodic conditions, H2O2 dissolv es GaAs chemically, and the surface appears rough but clean of other phases . The sulfate concentration near the surface increases to compensate for th e charge of the Ga3+ ions produced by dissolution. Under cathodic condition s, H2O2 is reduced electrochemically, bur chemical GaAs dissolution is neve r completely suppressed; both dissolution products are indirectly detected, the Ga3+ ions because they lead to an increase in the local sulfate concen tration and HAsO2 because part of it is reduced cathodically, giving island s of a solid arsenic hydride, most likely As2H2. Variations in the amount o f As2H2 and its surface coverage by adsorbed H and OH groups affect the H2O 2 reduction rate. A kinetic model is proposed for the interfacial chemistry and electrochemistry. Numerical simulations reproduce the main features of experimental current-potential scans, including the presence of a negative slope region related to oscillatory behavior.