Expressions were derived for thermal equilibrium concentrations of point defects, including neutral and charged species. These expressions were explicit functions of well-defined thermodynamic quantities which, in turn, yielded explicit expressions for the reaction constant, K, in the As4 pressure power-law representation of the point defect thermal equilibrium concentrations. It was recalled that such power laws had previously been of little quantitative value because the values of K were unknown. In the present derivation, emphasis was placed on the difference between the Gibbs free energies of an As atom in the interior of a GaAs crystal and in an As vapor-phase molecule, and on the role played by the crystal Fermi level. Numerical values were obtained for the thermal equilibrium concentrations of neutral and 3 negatively charged Ga vacancies (VGa0, VGa-, VGa2-, VGa3-), of neutral As vacancies, VAs0, and of the 2 neutral antisite defects, GaAs0 and AsGa0. The calculated thermal equilibrium concentration of the anion antisite defect, AsGa0, attained a peak value of about 1017/cm3 and was essentially temperature independent; in agreement with experimental observations. The thermal equilibrium concentrations of the triply negatively charged Ga vacancy were found to exhibit a temperature independence or a negative temperature dependence under strong n-doping conditions. That is, the concentration was either unchanged, or increased as the temperature was lowered. This behavior provided explanations for a number of outstanding experimental results. It required either the interpretation that VGa3- had attained a thermal equilibrium concentration at the start of each experiment, or required the assumption of mechanisms that involved point defect non-equilibrium phenomena. The calculated values of the thermal equilibrium concentrations of the triply negatively charged Ga vacancy were in agreement with available experimental results.

T.Y.Tan: Journal of the Physics and Chemistry of Solids, 1994, 55[10], 917-29