Formation of high-Sn content polycrystalline GeSn films by pulsed laser annealing on co-sputtered amorphous GeSn on Ge substrate**Project supported by the National Natural Science Foundation of China (Grant No. 61474094) and the National Basic Research Program of China (GrantNo. 2013CB632103).

Abstract

Polycrystalline Ge1−x (poly-Ge1−xSnx) alloy thin films with high Sn content (> 10%) were fabricated by cosputtering 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 Ge0.90Sn0.10 and Ge0.82Sn0.18 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-Ge1−xSnx by Raman spectra.