An X-ray diffraction study of the strain and structure of SiGeC/(100) Si alloys

High resolution X-ray diffraction studies were conducted on samples of Si_1-x-yGe_xC_y grown on (100)Si by chemical vapor deposition. The measurements were made with the diffractometer in its triple-axis configuration to produce reciprocal space maps. Films with compositions of approximately Si_0.78Ge_0.21C_0.01 and thicknesses ranging from 120 nm to 750 nm were found to be pseudomorphic with a tetragonal distortion strain, ∈_Τ, near 1%. The tetragonal strain was found to be independent of sample thickness. The strain in samples with compositions near Si_0.47Ge_0.50C_0.03 and thicknesses ranging from 61 to 115 nm were found to have tetragonal strain values greater than 2%. These strain measurements correlated well with ion channeling measurements. The experimental perpendicular lattice parameters were used to estimate the relaxed film lattice constants. These values fell midway between predicted values using Vegard's law for complete strain compensation by the carbon and no compensation by the carbon.