Miscibility of C in Si1-x-yGexCy thin films is systematically investigated by using the empirical interatomic potentials. The empirical potential approach is applied to calculate excess energies for Si1-x-yGexCy thin films incorporating interface lattice constraint due to S(0 0 1). In order to compare with experimental results, we employ the content values such as x = 0.13, 0.22, 0.27, 0.31, 0.35, and y = 0.019. The calculated results imply that the lattice constraint at the interface and Si-C interatomic bond formation dramatically reduce excess energies of Si1-x-yGexCy thin films by 20-30% of those in bulk state. Therefore, the lattice constraint promotes C incorporation in Si1-x-yGexCy thin films. Furthermore, segregation phenomena of Ge and C atoms in Si0.78Ge0.2C0.02 on Si(0 0 1) is clarified by Monte Carlo (MC) simulation taking into account surface and interface structures. The simulated results reveal that Ge atoms segregate in the topmost layer and C atoms accumulate in the second layer. These calculated results suggest that the lattice constraint at the interface enhance the miscibility of C in Si1-x-yGexCy thin films, whereas the miscibility tends to reduce near the surface because of the segregation of Ge and C atoms. (C) 2003 Elsevier Science B.V. All rights reserved.