Atomistic structure and strain relaxation in Czochralski-grown Si_xGe_1-x bulk alloys

The local atomistic structure in bulk Si_xGe_1-x alloys in the whole composition range 0 < × < 1 was investigated experimentally and theoretically. By extended X-ray absorption fine structure measurements in Czochralski-grown bulk SiGe crystals it is found that bulk SiGe is a random mixture and that the Ge-Ge, Ge-Si and Si-Si bond lengths maintain distinctly different lengths and vary in a linear fashion as a function of alloy composition across the entire composition range 0 < × < 1, in good agreement with expectations derived from the ab-inito electronic structure calculations. The results indicate that SiGe is a typical disorder material and that the bond lengths and bond angles are distorted with alloy composition in SiGe.