Mechanism of anodic oxidation of Hg_0.8Cd_0.2Te

The initial stages of Hg_0.8Cd_0.2Te anodization have been studied by electrochemistry and x‐ray photoelectron spectroscopy (XPS). Comparison of the polarization curves of HgCdTe, HgTe, and CdTe with XPS measurements of HgCdTe surfaces anodized to various potentials allows us to propose a possible model for the anodization. First the Hg‐rich surface layer formed by the bromine–methanol etch is removed at a potential of ∠−0.1 V vs SCE (standard calomel electrode). Upon oxidation of the Te²⁻ at ∠+0.35 V vs SCE in an aqueous solution (at ∠+0.6 V vs SCE in an ethylene glycol solution) the Cd²⁺ and Hg²⁺ ions are released, with the Cd²⁺ reacting with the Te⁴⁺ and O²⁻ to form CdTeO₃ and CdTe₂O₅. Some of the Hg²⁺ is incorporated into the oxide in analogous compounds, but most is driven into solution. The dissolution of Hg proceeds in advance of the Te⁴⁺/Te²⁻ interface, resulting in a depletion of Hg from the interfacial region of the semiconductor.