Lattice parameter in Si1-yCy epilayers:: Deviation from Vegard's rule

The precise C content of a series of Si1-yCy, epilayer samples (0 < y < 0.012)was determined by resonant backscattering experiments using a He-4(+) ion beam at 5.72 MeV. This beam energy is more suitable for the determination of the C content than the previously used 4.265 MeV. From the correlation of these investigations with x-ray diffraction experiments, a significant deviation of the lattice parameter variation in S1-yCy from Vegard's rule between Si and diamond or beta-SiC was observed, which amounts up to 30% or 13%, respectively, for y < 0.012. This negative deviation is in agreement with recent theoretical predictions by Kelires. (C) 1998 American Institute of Physics.