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 $263 cm−1.$