Depositing Au on TiAu from a Sulfite-Thiosulfate Electrolyte: Influence of the Electrochemical Process Conditions on the Properties of Gold Layers

Electrochemical deposition of gold from a sulfite-thiosulfate electrolyte was studied on GaAs–TiAu substrates using polarization curve measurements, gold layer morphology analysis (AFM), and current efficiency determination in the temperature range of 20–65 °C. It was found that increasing the temperature to 50–65 °C makes it possible to raise the gold deposition current density from 2 to 7 mA/cm2 while maintaining a current efficiency close to 100% and obtaining compact coatings with a surface root mean square roughness Sq of 6–8 nm. The activation energy of the process is 20–25 kJ/mol. It was shown that electrochemical conditioning of the electrolyte prevents sulfur precipitation, whereas the introduction of excess sulfite ions dissolves the sediment but leads to poorer coating quality. Thus, the feasibility of electrolyte regeneration has been demonstrated, and optimal gold deposition regimes have been determined: 7 mA/cm2 at 50 °C and 10 mA/cm2 at 65 °C.