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 electron microscopy, x-ray diffraction, and Raman scattering and modeled using 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. Experimental and theoretical results are compatible with Vegard's rule. To handle the large bond length distortions near C atoms properly, the valence-force field model used includes anharmonic effects via bond-length-dependent interatomic force constants which were determined from ab initio density-functional calculations. The dependence of the Raman spectra on strain and composition of Si1-x-yGexCy layers can be explained by the model calculations.