Thermodynamic modelling of miscibility in (InAs)_x(GaAs)_1−x solid solutions

Abstract

Current methods used to model the solution thermodynamics of III–V compound semiconductors involve the use of the valence force field as the molecular model and the regular solution model (with the temperature independent interaction parameter and underlying assumption of random mixing) as the engineering model. In this study, excess free energy models (with three or less adjustable parameters) are investigated to predict the solid–solid miscibility of (InAs) _x (GaAs)_{1− x} . The models investigated include the Porter/one-constant Margules (OCM) model, the two-constant Margules (TCM) model and the non-random two liquid (NRTL) model. These models are fit to excess free energy values derived from free energy change of mixing (variation with composition) data available from molecular simulations at different temperatures. The parameters in all the models have been found to be temperature dependent. The coexistence compositions are best predicted by the NRTL model, indicating the need to consider non-random mixing effects present in these solid solutions. The TCM model predicts better equilibrium composition data as compared to the OCM model.

Key Words:

• valence force field model
• order–disorder phase transition
• Margules models
• non-random two liquid model
• In _x Ga_{1− x} As

Acknowledgments

The author gratefully acknowledges the contributions of Mr Deepak Vadera, IIT Bombay. Computational resources have been provided by Computer Centre at Indian Institute of Technology Bombay and funding for the project is provided by the Department of Science and Technology, Government of India (Grant Number SR/S3/CE/50/2008).