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 Si1−yCy from Vegard’s rule between Si and diamond or β-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.