The Ge–C local mode in epitaxial GeC and Ge-rich GeSiC alloys

The Raman signature of the local Ge–C mode for substitutional C is identified as a narrow line (8 cm−1 full width at half maximum) near 530 cm−1 in alloy films of Ge1−yCy (0⩽y⩽0.07) grown on Ge (100) substrates by low-temperature (200 °C) molecular beam epitaxy. The intensity of the Ge–C line relative to the c-Ge line suggests that only a small fraction of the nominal C is in substitutional sites. In ternary alloys of Ge1−x−ySixCy with x=0.1 and 0.2 and y=0.03, the Ge–C mode disappears, suggesting a strong bias towards C bonding with Si as opposed to Ge. In Ge1−xSnx films the Ge–Sn mode is seen at 263 cm−1.