Determination of the GaPGaAs Solid Solution Interaction Parameter

Short-range order in GaPGaAs solid solutions (37.5, 41, and 54 mol% GaP) is studied by means of X-ray diffuse scattering measurements. The mixing energy of the system is found to be 1 kcal/mol for a short-range order existence in one of the sublattices by means of extrapolation of the long-wave Fourier-transform fluctuation of concentration (Cq) to the point q = 0. The total interaction parameter in the solid phase (B) including elastic interaction of the system amounts to 1.8 + 0.4C (C = mol% GaP). This parameter is used for phase diagram calculations, fitting best the experimental points of the solidus curve. The resulting interaction parameter in liquid phase (L) is found to be (4 – 2C) kcal/mol. The parameter B calculated by pseudopotential methods corresponds satisfactorily to the same parameter calculated above.