Formation of high-Sn content polycrystalline GeSn films by pulsed laser annealing on co-sputtered amorphous GeSn on Ge substrate

Polycrystalline Ge_1-xSn_x (poly-Ge_1-xSn_x) alloy thin films with high Sn content (> 10%) were fabricated by co-sputtering amorphous GeSn (a-GeSn) on Ge (100) wafers and subsequently pulsed laser annealing with laser energy density in the range of 250 mJ/cm² to 550 mJ/cm². High quality poly-crystal Ge_0.90Sn_0.10 and Ge_0.82Sn_0.18 films with average grain sizes of 94 nm and 54 nm were obtained, respectively. Sn segregation at the grain boundaries makes Sn content in the poly-GeSn alloys slightly less than that in the corresponding primary a-GeSn. The crystalline grain size is reduced with the increase of the laser energy density or higher Sn content in the primary a-GeSn films due to the booming of nucleation numbers. The Raman peak shift of Ge-Ge mode in the poly crystalline GeSn can be attributed to Sn substitution, strain, and disorder. The dependence of Raman peak shift of the Ge-Ge mode caused by strain and disorder in GeSn films on full-width at half-maximum (FWHM) is well quantified by a linear relationship, which provides an effective method to evaluate the quality of poly-Ge_1-xSn_x by Raman spectra.