Photoassisted Electrodeposition of CdTe Layer from Ammoniacal Basic Aqueous Solutions

Potentiostatic cathodic electrodeposition of CdTe on gold substrate under irradiation of visible light was studied using basic aqueous electrolytic baths in which Cd(II) and Te(IV) species were dissolved to form and ions, respectively. Both deposition current density and current efficiency for the CdTe deposition were enhanced by photoirradiation and, as a result, the time required for a given amount of deposition was dramatically shortened. The photoirradiation also resulted in a slight increase in cadmium content of the CdTe deposits and, in some cases, elemental Cd was deposited by underpotential codeposition. The cathodic polarization curve under pulsed photoirradiation showed a photoresponse in cathode current at potentials negative to the Nernst potential of CdTe deposition and the photoresponse was observed for wavelengths lower than that corresponding to the bandgap of CdTe, suggesting that the response was due to the CdTe itself growing on the cathode surface. The mechanism of the photoassist is discussed in terms of photoconduction of low-conducting CdTe semiconductors.