Thin Layer Electrochemical Studies of ZnS, ZnSe, and ZnTe Formation by Electrochemical Atomic Layer Epitaxy (ECALE)

ABSTRACTThin-layer electrochemical studies of the underpotential deposition (UPD) of Zn, Te, Se, and S on polycrystalline Au substrates have been performed. These studies were initiated to investigate the electrodeposition of ZnTe, ZnSe, and ZnS by electrochemical ALE (ECALE). Zn UPD on Au begins at -0.5 V and results in a coverage of 0.47 monolayer (ML). Te and Se atomic layers were formed using a two step process where bulk chalcogenide was removed by reduction, leaving the atomic layer. The reduction of the last atomic layer of Te or Se was not observed, regardless of how negative the potential was scanned. Sulfur atomic layers were spontaneously deposited below -0.6 V from a sulfide solution. Thermodynamic effects are clearly evident during the first monolayer of deposition. Zinc deposition onto Te, Se, and S coated electrodes occurs at progressively more positive potentials as the stability of the zinc compounds increase.This initial information was used to develop ECALE cycles for the compounds, and thin-films were formed by repeated application of the cycles. The dependence of the deposit coverage on the deposition potentials was examined and found to display the characteristic “S” curve of a surface limited process. In addition, the dependence of the coverage on the number of ECALE cycles performed was found to be near the ideal 0.5 ML per cycle for ZnSe and ZnS. The ZnTe coverage per cycle was less than expected indicating that further optimization of deposition conditions is needed.