The simultaneous realization of low thermal conductivity and high thermoelectric power factor in materials has long been the goal for the social use of high-performance thermoelectric modules. Nanostructuring approaches have drawn considerable attention because of the success in reducing thermal conductivity. On the contrary, enhancement of the thermoelectric power factor, namely, the simultaneous increase of the Seebeck coefficient and electrical conductivity, has been difficult. We propose a method for the power factor enhancement by introducing coherent homoepitaxial interfaces with controlled dopant concentration, which enables the quasiballistic transmission of high-energy carriers. The wavenumber of the high-energy carriers is nearly conserved through the interfaces, resulting in simultaneous realization of a high Seebeck coefficient and relatively high electrical mobility. Here, we experimentally demonstrate the dopant-controlled epitaxial interface effect for the thermoelectric power factor enhancement using our \"embedded-ZnO nanowire structure\" having high-quality nanowire interfaces. This presents the methodology for substantial power factor enhancement by interface carrier scattering.

[The 4th Thin Film and Surface Physics Division Award Speech] Methodology of thermoelectric power factor enhancement by controlling nanowire interface

A Si-based superlattice is one of the promising thermoelectric films for realizing a stand-alone single-chip power supply. Unlike a p-type superlattice (SL) achieving a higher power factor due to s...

High Thermoelectric Power Factor Realization in Si-Rich SiGe/Si Superlattices by Super-Controlled Interfaces.

We develop transparent epitaxial SnO2 films with low thermal conductivity and high carrier mobility by domain engineering using the substrates with low symmetry: intentional control of the domain size and the defect density between crystal domains. The epitaxial SnO2 films on r-Al2O3 (a low symmetry substrate) exhibit a twice higher mobility than the epitaxial SnO2 films on c-Al2O3 (a high symmetry substrate), resulting in twice larger thermoelectric power factor in the SnO2 films on r-Al2O3. This mobility difference is likely attributed to the defect density between crystal domains. Furthermore, both samples exhibit almost the same thermal conductivities (∼5.1 ± 0.4 W m−1 K−1 for SnO2/r-Al2O3 sample and ∼5.5 ± 1.0 W m−1 K−1 for SnO2/c-Al2O3 sample), because their domain sizes are almost the same. The uni-leg type film thermoelectric power generator composed of the domain-engineered SnO2 film generates the maximum power density of ∼54 μW m−2 at the temperature difference of 20 K. This demonstrates that a transparent film thermoelectric power generator based on the domain engineering is promising to run some internet of things sensors in our human society.

Carrier and phonon transport control by domain engineering for high-performance transparent thin film thermoelectric generator

Thermoelectric performance of p-type (Bi,Sb)2Te3 incorporating amorphous Sb2S3 nanospheres

Obtaining high thermoelectric performance has been the biggest historical challenge for thermoelectric power generation Here, we propose a methodology for thermoelectric power factor enhancement: thermal management with resonant level effect for simultaneous increase of electrical conductivity σ and Seebeck coefficient S Au crystals and Au impurities are introduced into SiGe Therein, (1) highly-conductive Au crystals increased σ (2) Au impurities brought about resonant level effect and phonon scattering, resulting in enhanced S and lowered thermal conductivity κ of SiGe (3) This κ distribution control brings the focus of temperature difference on SiGe parts with lowered κ, resulting in the availability of the enhanced S of SiGe parts as effective S of the entire nanocomposite Consequently, we achieved the highest S2σ at room temperature among SiGe-related materials ever reported Electronic structure calculation and measurement support the existence of resonant levels, which enhances S and lowers κ These results provide a new route to thermoelectric performance enhancement

Anomalous enhancement of thermoelectric power factor by thermal management with resonant level effect

We propose the methodology for thermoelectric power factor enhancement using nanoscale thermal management. The thermally managed composite is composed of a high electrical conductivity (σ) material...

Methodology of Thermoelectric Power Factor Enhancement by Nanoscale Thermal Management in Bulk SiGe Composites

Thin film thermoelectric materials have drawn much attention for realizing one-chip stand-alone power sources of internet of things devices. Here, we fabricate two types of the nanostructured Si films with high crystallinity: Si films containing β-FeSi2 nanodots with wider nanodot size distribution of ~5-120 nm and Si films containing α-FeSi2 nanodots with narrow size distribution of ~5-20 nm. The thermal conductivity of these films is lower than those of Si-silicide nanocomposite bulks. Interestingly, Si films containing β-FeSi2 nanodots shows about two times lower thermal conductivity than Si films containing α-FeSi2 nanodots. This is because the widely-size-distributed β-FeSi2 nanodots can effectively work as phonon scattering centers due to hierarchical architectures. These films also exhibited high power factor due to small amount of point defects and single crystalline epitaxial interfaces, despite iron silicide phase of nanodots. These detailed investigations will open a road for realizing the high-performance thin film thermoelectric materials.

https://iopscience.iop.org/article/10.7567/1347-4065/ab5b58/pdf

Kosei Mizuta

Papers

Anomalous enhancement of thermoelectric power factor by thermal management with resonant level effect

Methodology of Thermoelectric Power Factor Enhancement by Nanoscale Thermal Management in Bulk SiGe Composites

Nanostructural effect on thermoelectric properties in Si films containing iron silicide nanodots