期刊
ACS APPLIED MATERIALS & INTERFACES
卷 12, 期 22, 页码 25428-25434出版社
AMER CHEMICAL SOC
DOI: 10.1021/acsami.0c04982
关键词
thermoelectric material; superlattice; thermal conductivity; Seebeck coefficient; silicon; strain control; interface
资金
- JSPS KAKENHI, Japan [19H00853, 19K22110, 18J20160]
- Grants-in-Aid for Scientific Research [19K22110, 19H00853, 18J20160] Funding Source: KAKEN
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 strain-induced high hole mobility, in the n-type SL, the strain can degrade the power factor due to lifting conduction band degeneracy. Here, we propose epitaxial Si-rich SiGe/Si SLs with ultrathin Ge segregation interface layers. The ultrathin interface layers are designed to be sufficiently strained, not to give strain to the above Si layers. Therein, a drastic thermal conductivity reduction occurs by larger phonon scattering at the interfaces with the large atomic size difference between Si layers and Ge segregation layers, while unstrained Si layers preserve a high conduction band degeneracy leading to a high Seebeck coefficient. As a result, the n-type Si0.7Ge0.3/Si SL with controlled interfaces achieves a higher power factor of similar to 25 mu W cm(-1) K-2 in the in-plane direction at room temperature, which is superior to ever reported SiGe-based films: SiGe-based SLs and SiGe films. The Si0.7Ge0.3/Si SL with controlled interfaces also exhibits a low thermal conductivity of similar to 2.5 W m(-1) K-1 in the cross-plane direction, which is similar to 5 times lower than the reported value in a conventional Si0.7Ge0.3/Si SL. These results demonstrate that strain and atomic differences controlled by ultrathin layers can bring a breakthrough for realizing high-performance light-element-based thermoelectric films.
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