Electrodeposition of Dense Lead Telluride Thick Films in Alkaline Solutions

Abstract

Dense PbTe thick films were electrodeposited in alkaline solutions by an underpotential deposition mechanism of Pb on overpotential deposited Te. The composition of Pb is critical for the material properties. The composition of the electrodeposited PbTe films was Te-rich. Although the applied potential had no substantial effect on the Pb composition, it needs to be in the proper range (from −0.8 to −1.1 V vs. sat. Ag/AgCl) to avoid further reduction of Te to Te22− or keep the reduction of Te to Te22− at a low reaction rate. To deposit dense thick films the pH must be maintained in the range 10.5 to 12.3. Higher TeO32− concentrations and lower pH values decreased the Pb composition but increased deposition rates. Varying the TeO32− concentration changed the surface morphology of thick PbTe films, but all the thick films were found to be dense in the SEM cross section images. The ratio of EDTA4−/Pb2+ is also a critical effect, and the data showed that 7.5 was the optimum ratio with the given conditions, where the electrodeposited PbTe film was dense without cracks. A high deposition rate (approx. 163 μm/h) was achieved by high TeO32− concentrations (i.e., 550 mM) and at the deposition potential of 1.05 V vs sat. Ag/AgCl. The as-deposited PbTe films have relatively high Seebeck coefficient (i.e., 524 μV/K), but low electrical conductivity compared to bulk counterpart which might be attributed to lower crystallinity of PbTe with embedded Te nanocrystals.