Thermal conductivity and inelastic X-ray scattering measurements on SiGeSn polycrystalline alloy

Abstract

The impact of Sn on Si1-xGex through its thermal conductivity and phonon properties was investigated to develop an attractive material for thermoelectric devices. The Si-rich polycrystalline Si1-x-yGexSny alloy was synthesized by ball-milling technique. The as-synthesized alloy had substitutional Sn content of 1.60%, which it maintained as high as 0.54% after sintering at 1000 °C. The thermal conductivity was found to be reduced by the introduction of this tiny amount of Sn. Inelastic X-ray scattering measurements were carried out and we observed the longitudinal acoustic phonon mode superimposed along all crystallographic directions. In addition, the signal that originated from a local vibration at the Ge-related local structure was also successfully detected. It was found that the introduction of Sn affects the local vibration mode in the alloy. It is proposed that the incorporation of Sn atom into the local structure to make Ge–Sn pairs be considered to reduce the material’s thermal conductivity in addition to the mass difference effect.

SiSn mediated formation of polycrystalline SiGeSn

“…We previously reported the poly-Si 1-x-y Ge x Sn y synthesized by using the ball milling method, and that the introduction of Sn into Si 1-x Ge x successfully reduces the thermal conductivity. 24) However, the substitutional Sn content achieved in the poly-Si 1-x-y Ge x Sn y was only 0.54% because the synthesized polycrystalline powder was necessary to be sintered into pellets under high pressure at high temperature as high as 1000 °C. On the other hand, we also reported Sn nanodots (Sn-ND), which were formed on the Si substrate covered by the thermally oxidized SiO 2 layer, mediated formation of the poly-Ge 1-x Sn x layer at low temperature achieving high Sn content exceeding its solubility limit in Ge.…”

Ge1−x Sn x nanodots crystal nuclei for solid phase crystallization of poly-Si1−x−y Ge x Sn y

“…This study focused especially on reducing the thermal conductivity by the enhancement of phonon scattering. [8][9][10][11] Polycrystalline materials with a grain size larger than the mean free path of an electron and smaller than that of a phonon are effective in reducing the thermal conductivity. Therefore, poly-Si is expected to be a thermoelectric material.…”

“…Previous studies have shown that the thermal conductivity of polycrystalline Si 1−x Ge x can be further reduced by introducing Sn atoms, whose mass is 4.2 times greater than that of Si and 1.6 times greater than that of Ge, into the lattice substitution positions. 9,10) Similar to the introduction of Ge into Si, it is theoretically predicted that the substitution of Sn atoms into Si 1−x Ge x will result in lower thermal conductivity compared to Si 1−x Ge x . 18) This theoretical calculation shows that the introduction of Sn as well as a certain high Si content is necessary to reduce the thermal conductivity practically as the solid solubility limits of Sn in Ge and Si are very low.…”

Sn-incorporation effect on thermoelectric properties of Sb-doped Ge-rich Ge1−x−y Si x Sn y epitaxial layers grown on GaAs(001)

“…Apart from these applications, the Ge 1−x−y Si x Sn y is also expected to be used as a thermoelectric material 15,16) because it theoretically possesses a low thermal conductivity. 17,18) Highperformance thin-film thermoelectric devices, 19,20) e.g.…”