Semiconductor Properties of Passive Films on Zn, Zn‐Co, and Zn‐Ni Substrates

The semiconductor properties of passive films formed in alkaline aqueous solutions on Zn, Zn‐Co, and Zn‐Ni substrates were studied by electrochemical and photoelectrochemical methods. Substrate doping with Co and Ni leads to a homogeneous distribution of these elements in the passive oxide layer. The density and energy distribution of shallow donor states were determined from deviations from the ideal Mott‐Schottky behavior observed by electrochemical impedance measurements and from optical quantum efficiency experiments. The doping elements Co and Ni seem to generate deep donor levels, as indicated by impedance measurements. The inhibition effect of these doping elements on the corrosion rate of passive layers on Zn is interpreted in terms of transport processes within the oxide film.