Thermodynamic stability of Si1-x-yGexCy solid solutions is systematically investigated by excess energy calculations based on empirical interatomic potentials. The calculated excess energies for disordered Si1-x-yGexCy have positive values over the entire concentration range. This implies that Si1-x-yGexCy with a random distribution of Si, Ge and C is thermodynamically unstable at 0 K. The excess energies of Si1-x-yGexCy with sublattice ordering are also calculated. The calculated results imply that the ordered atomic arrangements reduce the excess energies and promote C incorporation in Si1-x-yGexCy because of increase of Si-C interatomic bonds. Furthermore, the excess energies of Si1-x-yGexCy 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 Si1-x-yGexCy. This gives one possible explanation for experimental findings where by the existence of Ge atoms prevents C incorporation in Si1-x-yGexCy growth. (C) 2002 Elsevier Science B.V. All rights reserved.