Experimental Determination and Thermodynamic Calcultions of the Relationship between Vapour Phase Composition and Mixed Crystal Composition in the Ga‐HCI‐PH₃‐AsH₃‐(NH₃)‐H₂ System

The relationship between the composition of GaAs 1– x P x layers and the composition of the vapour phase has been investigated experimentally and theoretically. Using K IRWAN'S equilibrium constants excellent agreement between calculated and experimental data is obtained over the whole composition range. Different models and parameters for the calculation of the soild solution activity coefficients result in only small differences for the calculated alloy composition so that no decision can be made from the experiments for one model to be preferred. Increasing addition of NH 3 to the vapour phase up to concentrations exceeding those of the crystal forming gases by an order of magnitude has no influence on the alloy composition, although the nitrogen concentration in the layers increases as deduced from the shift of the wavelength of the maximum photoluminescence intensity.