Synthesis of II-VI Semiconductors Thin Films By Ecald from Citric Buffer

Electrochemical Atomic Layer Deposition (ECALD) was proposed by Stickney and coworkers[1] to obtain low-cost production of structurally well-ordered II-VI compound semiconductors, such as transition metal chalcogenides, on polycrystalline as well as on single-crystal electrodes. The method is based on the alternate underpotential deposition (UPD) of atomic layers of the elements that form the compound. Underpotential deposition is the well-known phenomenon whereby the potential necessary to deposit one element onto a second element occurs before that necessary to deposit the element on itself. The phenomenon is surface limited, so that the resulting deposit is generally limited to one atomic layer.  Moreover, when the UPD is performed on a single crystal face the resulting deposit is epitaxial.

The free energy change involved in the compound formation is generally negative enough to produce the underpotential deposition of the metallic element on a layer of the previously deposited nonmetallic element, and vice versa. The number of cycles, which determines the thickness of the deposits, can be repeated as many times as desired to obtain deposits of practical importance. By limiting depositions to single atomic layers, no three dimensional growth is promoted and epitaxy should result.

Once the deposit is formed, the amount of the elements deposited is determined from the charge involved in their stripping. Such investigations always confirmed the stoichiometric ratio of the elements forming the compound.

The fundamental object to the method is the necessity of singling out the proper electrochemical conditions to be used, i.e. potentials, reactants, electrolytes and pH. Moreover, being the method based on surface phenomena, the electrochemical conditions are also dependent on the substrate used. Here, the first results of the electrodeposition of CdSe and ZnSe on polycrystalline gold from citric buffer are reported.

Acknowledgments

This work was supported by the Polish National Center of Science under grant 2011/01/D/ST5/05743.

1.             Gregory, B.W. and J.L. Stickney, Electrochemical atomic layer epitaxy (ECALE). Journal of Electroanalytical Chemistry, 1991. 300(1-2): p. 543-561.