For the theory of electrochemical analysis, a kinetic model that considers the ion transport limitations near the cathode of electrode is based upon a generalized Butler-Volmer equation and has been modified in theory and developed. The subjects of this study are the investigation of the kinetics mechanism of CdTe electrodeposition from an aqueous solution containing CdSO4, TeO2, and H2SO4 in cyclic voltammetry and applied to the optimal control of the composition and stoichiometric deviation of CdTe thin film by electrodeposition. The computer simulation is performed to understand the influences of electrodeposited parameters in the process, such as deposition temperature, pH value and concentrations of Cd2+ and HTeO2+ ions, is one of the focuses in this study.
In this investigation, a novel electrochemical method for simultaneously measuring diffusion coefficient and ion transference number is applied in the simulation of CdTe electrodeposition for the first time. From the fitting of the experimental data, the values of the thermodynamic, kinetic and mass transport parameters of the electrodeposition process are obtained. In addition, the modified Butler-Volmer model predicts the potential of perfect stoichiometry (PPS) for electrodeposition of CdTe thin film, and a good agreement has been found between the calculated and experimental results. It also predicts the composition of electrodeposits for the electrodeposition of CdTe and other II-VI and III-V compounds from solutions containing reducible ions. Furthermore, the one that is worth mentioning in this investigation, a novel algorithm of stoichiometric deviation is also developed and applied to the electrodeposition for the first time. With the change of the parameter, the deviation of stoichiometry can be estimated accurately.
The simulated results of mathematical model are verified experimentally using electrodeposition and can obtain two aspects. They are the accurate potential perfect stoichiometry (PPS) in which the intrinsic CdTe thin film can be electrodeposited and the stoichiometric deviation which can be dominated accurately in the adjustment of electrodeposited potential. Besides, the native non-degenerate p-type and n-type CdTe thin film can also be deposited. At PPS, well-connected granular CdTe thin films can be deposited and are predicted to be intrinsic, but are slightly p-type due to cadmium vacancies (VCd). The conversion of conductive type occurs only by defect redistribution and local defect reactions after annealing; the converted n-type layer shows lower resistivity and higher mobility. A film annealed at 350oC exhibits excellent crystallization.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0202109-025446 |
| Date | 02 February 2009 |
| Creators | Yang, Shu-Ying |
| Contributors | Yeu-Long Jiang, Yuh-Fung Huang, Jung-Chuan Chou, Wei-Chou Hsu, Yeong-Her Wang, Herng-Yih Ueng |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0202109-025446 |
| Rights | not_available, Copyright information available at source archive |
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