Cathodic Deposition and Characterization of Metallic or Semiconducting Binary Alloys or Compounds

Abstract

The conditions to be met to achieve cathodic deposition of compounds or alloys of well-defined stoichiometric composition are discussed. If the deposition rate constants of the components are of the same order, two classes of codeposition have to be distinguished, differing in whether the difference in electrode potential of the individual components is larger (class I) or smaller (class II) than the shift in electrode po,tential of either component as a result of compound or alloy formation. In the former case the potential of the deposit is determined by the less noble component over the entire composition range, the deposition potential shifting monotonically with composition. In the latter case the role of potential-determining species may shift Irom one component to the other at an intermediate composition, the deposition potential at this composition being more positive than that of either of the components when deposited individually. For class I, quasi rest potentials uniquely characterize the deposits. For class II different deposits may have the same quasi rest potential. Compounds are stable in electrolytes with large concentrations of the normal ions of one of the components in the absence of nonmetal complexes necessary to make cathodic deposition of the compounds possible. If the potential is not determined by adsorbed noncomponent species, the potentials are determined by the normal ions, the concentrations of which are linked by solubility products.Cathodic codeposition of different elements with formation of metallic alloys or compounds from aqueous electrolytes has been known for a long time (1). Nonmetals such as S, So, To, and As and semimetals such as Sb and Bi can be deposited cathodically from solutions of complex ions or molecules (2) and cathodic codeposition of one of these elements and metallic elements with the formation of compounds may therefore also be possible. Examples are found in the formation of CdSe and Ag2.Se (3), Ni-P and Co-P alloys (4), and .Interactions between the components in the deposit usually shift the deposition potential of the deposit to values that are positive relative to the deposition potential of the less noble component (induced codeposition) (6). In some cases, e.g., for Ni, Sn alloys (7), the deposition potential is positive even relative to that of the noble component, an effect that so far remained unexplained (8).In this paper the thermodynamic basis of codeposition and the nature of the potential-determining species are considered and on this basis an explanation of the observed effects is arrived at. No attention is paid to the possibility of hydrogen discharge.

Emerging materials for solar cell applications: electrodeposited CdTe. Final report, February 14, 1979-February 14, 1980

“…Et is found to be 0.55 eV from the slope of this curve. The trap dP.n~it.y calculated 15 17 from Equation (4) and (3) is approximately 7xl0 using N = 8xl0 /cm3 c and Et= 0.55 eV. A mobility of 1000 cm.…”

Electrochemically Fabricated Alloys and Semiconductors Containing Indium

“…38) Because nonmetals such as S and Se, and semimetals such as As, Sb, and Te can be deposited cathodically from solutions of complex ions or molecules, cathodic codeposition of one of these elements and of metallic elements may also be possi-ble. 29,[39][40][41] In the electrodeposition of an alloy in which one elementary component is much nobler than the other, a complexing agent must be added in order to equalize the deposition potentials. Acetate, citrate, tartrate, cyanide, EDTA (ethylenediamine tetraacetic acid), triethanolamine, and CTAB (cetyltrimethylammonium bromide) are used as complexing agents.…”

From Metals to Semiconductors: Challenges in Electrodeposition for Photovoltaic Applications

“…The deposition potentials of the non-metals are usually widely different from those of the metals. General principles of binary component electrodeposition were introduced by Kröger to account for the departure from ideality of the addition of partial currents during deposition of binary alloy or compounds (17). Most of the semiconductor compounds have a highly negative Gibbs free energy of formation, which is generally higher than for pure metallic alloys.…”

“…Most of the semiconductor compounds have a highly negative Gibbs free energy of formation, which is generally higher than for pure metallic alloys. This usually shifts the cathodic potential for the incorporation of the less noble component to a more positive value (17,18). The example of Cd-Te codeposition will be developed in the following paragraph.…”

“…Some investigations were carried out in ammoniacal solutions (29). However most of the studies have investigated the deposition from acidic aqueous solutions containing Te(IV) species as HTeO 2 + in the presence of Cd 2+ ions at 70-80°C (17,18). Electrodeposition occurs in two successive reduction steps: with decreasing potentials, the first step is the four-electron reduction of (HTeO 2 + ) to elemental tellurium, followed by the two-electron reaction with Cd 2+ ions to form CdTe (17,18,21).…”