Reduced thermal conductivity of a Ge 1−x Sn x layer formed on a self-assembled Sn nanodot template

Self-assembled Sn nanodots were formed on SiO 2 and the crystallinity and Sn composition of a Ge 1−x Sn x polycrystal formed on the Sn nanodots were evaluated. The average diameter of the Sn nanodots was 17.1 nm, and their density was 1.5 × 10 9 cm −2 . Raman spectroscopy revealed that the crystallinity of Ge 1−x Sn x increased from 52.29% to 86.82% as the Ge deposition temperature increased from 100 °C to 225 °C. However, agglomeration degraded the surface roughness when the Ge deposition temperature was high. By contrast, the Sn composition reduced from 12.84 to 4.78%. For both high Sn composition and a flat surface, lowering the Ge deposition temperature was found to be crucial. The impact of the crystallinity and Sn composition on thermal conductivity was investigated using the time-domain thermoreflectance method. Thermal conductivity increased with the increase in crystallinity, and it reached 2.305 W m −1 K −1 for Ge 1−x Sn x with a crystallinity of 86.82%. Ge 1−x Sn x alloy had lower thermal conductivity than that of Ge at the same crystallinity.