GaAs/H_2O_2 Electrochemical Interface Studied In Situ by Infrared Spectroscopy and Ultraviolet-Visible Ellipsometry Part I: Identification of Chemical Species

摘要

Chemical species at the electrochemical interface between n-GaAs(100) and H_2O_2 in 0.5 M H_2SO_4 are identified by in situ infrared spectroscopy and in situ ultraviolet-visible ellipsometry. Under anodic conditions, H_2O_2 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 Ga~(3+) ions produced by dissolution. Under cathodic conditions, H_2O_2 is reduced electrochemically, but chemical GaAs dissolution is never completely suppressed; both dissolution products are indirectly detected, the Ga~(3+) ions because they lead to an increase in the local sulfate concentration and HAsO_2 because part of it is reduced cathodically, giving islands of a solid arsenic hydride, most likely As_2H_2. Variations in the amount of As_2H_2 and its surface coverage by adsorbed H and OH groups affect the H_2O_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.