Systematic theoretical investigations of miscibility in Si _1-x-y Ge _x C _y thin films

Miscibility of C in Si _1-x-y Ge _x C _y thin films is systematically investigated by using the empirical interatomic potentials. The empirical potential approach is applied to calculate excess energies for Si _1-x-y Ge _x C _y thin films incorporating interface lattice constraint due to Si(001). 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 Si _1-x-y Ge _x C _y thin films by 20-30% of those in bulk state. Therefore, the lattice constraint promotes C incorporation in Si _1-x-y Ge _x C _y thin films. Furthermore, segregation phenomena of Ge and C atoms in Si _0.78 Ge _0.2 C _0.02 on Si(001) 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 Si _1-x-y Ge _x C _y thin films, whereas the miscibility tends to reduce near the surface because of the segregation of Ge and C atoms.