Studies of oxidation behaviors of CdTe in ammoniacal basic electrolytes

The time variations in the electrode potential and mass of an electrodeposited CdTe layer when immersed in a deposition bath under an open-circuit condition were examined using an electrochemical QCM in order to observe the oxidation behavior due to dissolved oxygen. The morphology, composition, and crystallinity of the CdTe layer were also examined by SEM, EPMA, and XRD measurements. In the early stage of immersion, mostly only Cd atoms in the CdTe were found to dissolve from the zinc blende-type CdTe lattice, keeping the flat and smooth surface morphology intact. Then, the remaining Te formed a lattice of elemental Te and covered the CdTe layer. The electrolyte could penetrate the Te layer and access the CdTe layer's surface because the Te layer was porous due to the elution of Cd atoms. Therefore, the preferential dissolution of Cd species continued to occur, and finally, only the porous Te layer remained on the substrate. This dissolution of CdTe supports the validity of the potential–pH diagram of the Cd–Te–NH3–H2O system.