Theoretical investigations of thermodynamic stability for Si 1− x− yGe xC y

Abstract

Thermodynamic stability of Si 1− x− y Ge x C y solid solutions is systematically investigated by excess energy calculations based on empirical interatomic potentials. The calculated excess energies for disordered Si 1− x− y Ge x C y have positive values over the entire concentration range. This implies that Si 1− x− y Ge x C y with a random distribution of Si, Ge and C is thermodynamically unstable at 0 K. The excess energies of Si 1− x− y Ge x C y with sublattice ordering are also calculated. The calculated results imply that the ordered atomic arrangements reduce the excess energies and promote C incorporation in Si 1− x− y Ge x C y because of increase of Si–C interatomic bonds. Furthermore, the excess energies of Si 1− x− y Ge x C y increase with Ge content x when C content y remains constant; this is because an increase of Ge content introduces a large strain energy in Si 1− x− y Ge x C y . This gives one possible explanation for experimental findings where by the existence of Ge atoms prevents C incorporation in Si 1− x− y Ge x C y growth.