Thermodynamic Database for Alloy Semiconductor Systems.

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III-V compound semiconductors (III=AI, Ga, In : V=P, As, Sb) have various outstanding properties which can not be obtained by Si semiconductor. Furthermore, mixture of these compounds which is called as III-V crystal alloy semiconductor gives possibilities to control its physical properties arbitrarily such as the band gap energy and the lattice constant by its composition. Therefore, III-V crystal alloy semiconductors are of great significance for opto-electronics and high-speed devices. In order to realize the desirable properties, i.e., to create the crystal alloy with appropriate composition by Liquid Phase Epitaxy (LPE) method under the condition of near phase equilibria, phase diagrams are indispensable for controlling their microstructures and compositions. However, it was reported that a thin epitaxial layer on a substrate exhibited completely different phase equilibria from those of bulk materials, for instance, deviation of equilibrium composition, formation of unexpected pha … More ses and so on. In this research, thermodynamic analysis on the phase equilibria of III-V crystal alloy semiconductor was carried out based on the thermodynamic data and experimental results. Then, thermodynamic database has been established for calculating the phase equilibria of both bulk and thin layer materials.Gibbs energies of the liquid phase and the compound are described by the sub-regular solution approximation and the two-sublattice model respectively. The strain energy was taken into account for calculating the stability of a thin epitaxial layer grown on a substrate.Thermodynamic parameters of eleven ternary systems have been evaluated and thermodynamic database for III-V alloy semiconductors has been constructed with or without taking account of a strain energy between a epitaxial layer and a substrate. The effect of the strain energy which is caused from the epitaxy between a crystal layer and a substrate can be seen, for instance, when a GaAs-GaSb crystal alloy is grown epitaxially on the (100) plane of lnP substrate. According to the result of calculations, unexpected homogeneous phase appears when its thickness is him and its composition is 5 lmol% GaAs which corresponds to the lattice matching composition. This is in good agreement with the experimental result of LPE by Quillec et al. The results of calculations for various combinations between thin layers and substrates show that phase stability of an epitaxial layer depends on the lattice constant and the crystal orientation of the substrate and on the thickness of the epitaxial layer. Less