Electroless plating of iron-group metals and electrochemical comparison for thermoelectric contacts

Bismuth telluride and lead telluride are typical thermoelectric semiconductors that are metallized for electrical contacts before being assembled into devices. In this study, three iron-group metals of nickel cobalt iron, were chemically plated on n-type bismuth telluride as the prospective contact material for adhesion and barrier in soldering connection with copper. Aluminum was used as the sacrificial anode to ensure iron deposition. The sensitization in borohydride solution facilitated the subsequent plating of metals. The plating rates were determined by gravimetric method. The crystalline structure and morphology of films were characterized. Electrochemical polarizations were undertaken to compare the driving force among three plating reactions through the reduction of metallic cations and the oxidation of hypophosphite anions with the mixed potential theory. The heterojunction of bismuth telluride with copper was fabricated by reflow soldering with Sn 95 Sb 5 foil, and the interfacial resistivity was evaluated by multiple resistance measurements across the junction.