Metal submonolayers on Hg-Zn-Te alloys: Electrochemical and electrolyte electroreflectance studies

Electrodeposition of Ag and Cu in the dark at mercury-zinc-telluride alloys (HZT) is studied by electrochemistry and electroreflectance. The specific importance of submonolayer deposits on the behavior of electrolyte-HZT junctions is evidenced. The morphology of the deposits depends drastically on the experimental conditions and especially on the applied potential. Cu and Ag deposits are done in the dark and in underpotential regime like that for metal substrates. However, the electrochemical behavior of these layers is completely different from what is observed with metal electrodes. Electroreflectance spectra recorded with metal-coated alloys present an extremely specific behavior, the spectrum relative to the $E_1$ transition of the substrate vanishing and a new broad feature being created. This phenomenon is especially important for alloys with composition 0.3≤x≤0.7 whereas for binary alloys such as ZnTe, HgTe, and GaAs it does not exist. A specific chemical interaction between Ag and Cu and the HZT substrate is postulated, based on electrochemical and electroreflectance results, which depends strongly on the chemical composition of the substrate.