Unstable Regions in Type A1-x-yBxCyD III-V Quaternary Solid Solutions Calculated with Strictly Regular Solution Approximation

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Abstract
Solid-state immiscibility in type A1-x-y B x C y D III-V quaternary solid solutions is analyzed on the basis of the strictly regular solution approximation. The calculated spinodal isotherms for various temperatures show that the existence of unstable regions, and hence miscibility gaps, which are always found on the ternary side, is a common feature of these quaternaries, although the extent of these regions depends strongly on the particular quaternary system and the temperature. Fairly large unstable regions are expected for quaternary systems with mixing on group V element sublattices at ordinary growth temperatures. These results indicate the limitations of these quaternaries for practical applications such as optical sources.