Unstable Regions in III–V Quaternary Solid Solutions Composition Plane Calculated with Strictly Regular Solution Approximation

The behavior of unstable regions in the composition plane for III–V quaternary solid solutions made from among Al, Ga, In, P, As and Sb is analyzed, based on the strictly regular solution approximation for solid solutions. Temperature dependences of spinodal isotherms at 400–1000°C show that unstable regions cover a wide range of compositions. It is suggested that composition ranges exist where the spinodal temperature exceeds the melting point, so that such solid solutions can never be grown by near-equilibrium growth methods. Positions of quaternary critical points in the composition plane are also shown.