Thermodynamic Properties of Nonstoichiometric Cadmium Telluride and Defect Chemistry Analysis.
This dissertation is an investigation of nonstoichiometric CdTe(c) based upon experimentally measured tellurium partial pressure data. The partial pressures and stability limits of CdTe(c) on Te-rich side have been obtained through the optical absorbance measurements of the vapor phase. The theoretical monatomic absorption line profile is applied to fit the Cd(g) optical absorbance. A foreign gas (Te _2(g)) broadening coefficient of the Cd(g) absorption line is obtained from measured partial pressures of Te_2(g) over CdTe, measured optical density at the 2288 A, and calculated Cd(g) line profile. A discrepancy between the measured stability limits of CdTe(c) and the published hole concentration data is interpreted as a self-compensation phenomenon. A statistical thermodynamic analysis is carried out for a model of Te-rich CdTe in which doubly ionizable Cd-vacancy acceptor and singly-ionizable Te on Cd-site donor are assumed. The equilibrium equations obtained are applied to Te-saturated CdTe, for which the partial pressure of Te_2 (g), the atomic fraction of Te and the hole concentration are known over a range of temperature. The enthalpies and excess entropies of formation of the un-ionized Cd -vacancy and un-ionized Te on Cd-site defects are obtained.
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- Engineering: Materials Science; Physics: Condensed Matter