Numerical Simulations and Controllable Stoichiometry on Cadmium Telluride Compound by Electrochemical Deposition

Cadmium telluride has attracted much interest because of its varied applications for the last couple of decades. It is recognized as a highly miscellaneous II-VI narrow band-gap (Eg = 1.45 eV) binary compound semiconductor, and is the only material which can be in both n- and p-conductivity types. Electrochemical deposition is a very attractive approach due to its low cost technique. The generalized Butler-Volmer and Nernst equations describe ion transport limitations near the cathode have been developed, and a simple electrode kinetic model has also been applied for the electrochemical deposition. CdTe of well-defined composition has been deposited cathodically from an aqueous solution of CdSO4 and TeO2. The solution is postulated here as a regular associated solution (R.A.S.). Approximate activities are derived assuming regular ternary solution behavior for the cadmium, tellurium, and cadmium telluride species. On the theoretical approach, the mathematical model can be used to make a convenient algorithm to numerically simulate current-potential relationship, ionic concentration profile, and calculate the composition existing at the surface of cadmium telluride deposit for any deposition potential. The precise control of stoichiometry is very important to investigate the intrinsic properties. It could be obtained by carefully controlling the growth parameters, for instance, the deposition potential, temperature, ion concentrations, and pH value.