The Induced Electrochemical Codeposition of Cu-Ge Alloy Films

Various examples of induced codeposition have been over time reported in the literature and partly understood. In particular, Brenner discussed as early as 1963 in his book "Electrodeposition of alloys" evidence of the induced deposition of Germanium; attempts to understand such mechanism however are lacking. In this work, the electrochemical co-deposition of Cu-Ge thin films from an alkaline tartrate-complexing electrolyte was investigated by combined cyclic voltammetry and quartz crystal microbalance of the unitary and alloy electrolytes. Ge undergoes reduction from Ge4+ (GeO32−) to Ge1− (GeH) in a two-step process and forms a self-limiting deposit, the thickness of which is a function of the Ge ion concentration and pH. Cu2+ deposition is strongly inhibited by the presence of Ge species above −1.2 V Ag/AgCl, while at more negative potentials a signature of alloy codeposition is present, in parallel with hydrogen evolution. Oxygen deposition is significant when Ge is at or above 25 at%. Induced codeposition is rationalized in terms of the activation of the Ge-H bond by Cu, resulting possibly in the formation of adsorbed species containing H-Cu-Ge, whereby H is dissociated, resulting in alloy growth in parallel with formation of a significant amount of H2 gas.