LATTICE DISTORTION IN A STRAIN-COMPENSATED SI1-X-YGEXCY LAYER ON SILICON

A number of Si1-x-yGexCy layers with different concentrations of Ge an d C were grown by molecular-beam epitaxy on a Si(001) substrate to inv estigate the possibility of strain compensation. The layers were chara cterized by transmission electron microscopy, x-ray diffraction, and R aman scattering and modeled using a valence-force field model. For a [ Ge]/[C] ratio of approximately 10, the lattice constant in the growth direction is equal to that of the substrate, indicating the absence of macroscopic strain. Experimental and theoretical results are compatib le with Vegard's rule. The bond lengths in the alloy exhibit a signifi cant relaxation away from the ideal ''chemical'' value as given by the sum of the corresponding covalent radii. The measured shifts of the R aman frequencies relative to the constituents cannot be understood in a straightforward description based purely on the softening or hardeni ng of the interatomic bonds as deduced from the Gruneisen parameters.