Structural analysis of SiGe and SiGeC alloys by ab initio total-energy calculations

The structural properties of SiGe and SiGeC alloys are studied by ab initio total-energy calculations. It is found from these calculations that the Ge cluster is a stable structure in a SiGe alloy. Furthermore, it is also demonstrated that Vegard's law is valid in a SiGeC system whose C content is less than 3%. The total-energy calculation of the Si0.72Ge0.25C0.03 alloy in which the number of Ge-C bonds around a C atom varies shows that the energy increases on increasing the number of Ge-C bonds. The mechanism of this increase is considered, taking into account the cohesive energy difference of the SiC and GeC alloys and the atomic configuration around the C atom.