Phase equilibria in III–V quaternary systems—application to Al-Ga-P-As

A method is given to calculate liquidus-solidus phase diagrams involving quaternary III–V solid solutions of the type A_xB_{1 ? x}C_yD_{1 ? y}. The calculation treats the mixture of A and B atoms on the group III sublattice and C and D atoms on the group V sublattice as strictly regular and the quaternary liquid solution as simple. The input parameters for the calculation are obtained from existing analyses of the binary and ternary boundaries of the phase diagram.Experimental liquidus and solidus data along several Al isoconcentration curves on the 900 ° and 1000 °C isotherm surface are presented for the Al-Ga-P-As system. The liquidus data are obtained by liquid observation and saturation techniques and solidus compositions determined on self-nucleated cyrstals and on mixed crystal layers grown on GaP substrates. The experimental results are consistent with the calculated phase diagram for this system.