MICROSCOPIC THERMODYNAMIC MODELS OF QUASIBINARY SEMICONDUCTOR SOLID SOLUTIONS
A review of microscopic models describing the thermodynamics of semiconductor quasibinary solid solutions of type А3В5 and А2В6 is presented. The main existing approaches areanalyzed. The structural model with a tetrahedron as the main cluster takes into account the relaxation of only the central atom and differs from the earlier models in the way of estimating the excess free energy. This makes it possible to evaluate the irregularity of solid solutions in a more objective way. Such structural model gives overestimated results in constructing phase diagrams, because it neglectes higher order relaxation. The model with larger main clusters takes into account relaxation to the second coordination sphere and in some cases gives good agreement with the experimental results. But this model leads to rather complex and cumbersome calculations of the total energy of the system. The third model is a model of an infinite disordered solid solution in the form of a supercell with periodic boundary conditions. For this model, results are presented for averaged distances to the first and second nearest neighbors and the width of the distribution of bonds for the first nearest neighbors for materials of the III–V and II– VI groups. A comparison of the calculated phase diagrams with experimentally determined regions of immiscibility is given.
Authors: I. A. Cheremukhina
Keywords: Solid solution, cluster, coordination sphere, short-range-order, mixing enthalpy, entropy, phase diagram
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