ATOMIC-STRUCTURE AND LATTICE-DYNAMICS OF STRAIN-COMPENSATED SI1-X-YGEXCY LAYERS

The local atomic structure and lattice dynamics are studied for strain -compensated Si1-x-yGexCy layers grown by molecular beam epitaxy on Si (001) substrates. The layers were characterized by transmission elect ron microscopy, x-ray diffraction, and Raman scattering and modeled us ing a valence-force field model. For a [Ge]/[C] ratio of approximately ten, the lattice constant in the growth direction is equal to that of the substrate, indicating an absence of macroscopic strain. Experimen tal and theoretical results are compatible with Vegard's rule. To hand le the large bond length distortions near C atoms properly, the valenc e-force field model used includes anharmonic effects via bond-length-d ependent interatomic force constants which were determined from ab ini tio density-functional calculations. The dependence of the Raman spect ra on strain and composition of Si1-x-yGexCy layers can be explained b y the model calculations.