Structure of oxygen-related defect centers in Ge_1-xSi _x alloys studied by extended energy-loss fine structure analysis

Oxygen atoms dissolved near the surface regions in Ge_1-xSi _x alloys were studied by extended energy-loss fine structure (EXELFS) analysis using electron energy-loss spectroscopy (EELS) and the local structures around oxygen were determined. Oxygen preferentially formed Si-O-Si centers, rather than Si-O-Ge or Ge-O-Ge. The O-Si bond length was increased with decreasing the Si content, in accordance with the increase in the Si-Si, Si-Ge and Ge-Ge bond lengths. The increase in O-Si bond length is much more significant than that expected from the changes in Si-Si, Si-Ge and Ge-Ge bond lengths. The derived local atomic configuration of the Si-O-Si center changed with increasing Si content, which corresponds well to the surface oxidization process of crystalline silicon.