Raman scattering study of amorphous GeSn films and their crystallization on Si substrates

• The ratio RSn/Ge in Raman spectra of amorphous GeSn increases linearly with Sn contents ranging from 0.06 to 0.2.
• Relative lower annealing temperature benefits high Sn content crystalline GeSn films with smooth surface.
• Polycrystalline GeSn films with substitutional Sn content of 0.07 are achieved by rapid thermal annealing at 400 °C.

The dependence of Raman scattering spectra on Sn composition in the amorphous Ge1-xSnx films deposited on Si(001) substrates by magnetron sputtering is investigated. Two broad phonon scattering peaks are clearly observed, which are attributed to the disordered SnSn and GeGe bonds, shifting to lower wavenumbers with the increase of Sn content. The ratio of integrated intensity of SnSn to GeGe modes increases linearly with Sn content in the range of 0.06 to 0.2. With rapid thermal annealing, although the critical crystallization temperature becomes lower for higher Sn content amorphous GeSn, severe Sn segregation occurs for all of the samples. Relative lower crystallization temperature is proved to be beneficial for tailoring high Sn content crystalline GeSn films. Polycrystalline GeSn alloys with maximum substitutional Sn content of 0.07 are achieved with an annealing temperature of 400 °C.