Reduced thermal conductivity of a Ge_1−xSn_xlayer formed on a self-assembled Sn nanodot template

Abstract

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.

Thermoelectric Efficiency of Epitaxial GeSn Alloys for Integrated Si-Based Applications: Assessing the Lattice Thermal Conductivity by Raman Thermometry

“…Still, the thermal properties of GeSn alloys have not been explored yet, and their potential as CMOS-integrable TE materials remains unknown. The few existing experimental reports deal with amorphous or polycrystalline films, , while, ideally, good thermoelectric materials should be crystalline, where phonon scattering occurs without disrupting the electrical conductivity …”

“…15 These successes were enabled by the progress made in the GeSn epitaxy on Ge/Si substrates 16,17 as CMOS-integrable TE materials remains unknown. The few existing experimental reports deal with amorphous or polycrystalline films, 18,19 while, ideally, good thermoelectric materials should be crystalline, where phonon scattering occurs without disrupting the electrical conductivity. 20 In this work, the TE properties of high-quality GeSn epitaxial layers on Si are investigated.…”

Inorganic thermoelectric materials: A review

“…For instance, Tenanodots in ZnO/BTS interfaces, enhanced σ and S due to the quantum confinement effect, 70 Ge-nanodots in Sibased material reduced κ t to ~1.2 Wm −1 K −1 , 71 Aunanodots in Bi 2 Te 3 nanocomposites reduced κ lat to ~0.47 Wm −1 K −1 , 72 and Sn-nanodots in Ge reduced κ t to 2.305 Wm −1 K −1 . 73 Likewise, nanowires with small electron effective mass and a diameter greater than 5 nm could attain low κ t as well as high PF, 69 whereas, superlattices enhance the performance of TE materials by reducing the κ t by controlling the transport of phonons and electrons without any effect on PF. 33 For instance, Subramanian et al showed that the multiple-quantumwell of Bi 2 Te 3 -Sb 2 Te 3 superlattices provide a high ZT value of ~2.4 by reducing κ t .…”

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.…”