Large Thermoelectric Figure-of-Merits from SiGe Nanowires by Simultaneously Measuring Electrical and Thermal Transport Properties

• Published in: Nano letters 2012-06, Vol.12 (6), p.2918-2923
• Main Authors: Lee, Eun Kyung, Yin, Liang, Lee, Yongjin, Lee, Jong Woon, Lee, Sang Jin, Lee, Junho, Cha, Seung Nam, Whang, Dongmok, Hwang, Gyeong S, Hippalgaonkar, Kedar, Majumdar, Arun, Yu, Choongho, Choi, Byoung Lyong, Kim, Jong Min, Kim, Kinam
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Correlation; Cross-disciplinary physics: materials science; rheology; Crystal structure; Electron Transport; Energy Transfer; Exact sciences and technology; Germanium - chemistry; Hot Temperature; Lattice dynamics; Macromolecular Substances - chemistry; Materials science; Materials Testing; Molecular Conformation; Nanocrystalline materials; Nanoscale materials and structures: fabrication and characterization; Nanostructures - chemistry; Nanostructures - ultrastructure; Nanowires; Particle Size; Phonons; Phonons in low-dimensional structures and small particles; Physics; Quantum wires; Retarding; Scattering; Silicon - chemistry; Silicon germanides; Surface Properties; Thermal Conductivity; Thermal properties of condensed matter; Thermal properties of small particles, nanocrystals, nanotubes; Thermoelectricity; Transport
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl300587u

The strongly correlated thermoelectric properties have been a major hurdle for high-performance thermoelectric energy conversion. One possible approach to avoid such correlation is to suppress phonon transport by scattering at the surface of confined nanowire structures. However, phonon characteristic lengths are broad in crystalline solids, which makes nanowires insufficient to fully suppress heat transport. Here, we employed Si–Ge alloy as well as nanowire structures to maximize the depletion of heat-carrying phonons. This results in a thermal conductivity as low as ∼1.2 W/m-K at 450 K, showing a large thermoelectric figure-of-merit (ZT) of ∼0.46 compared with those of SiGe bulks and even ZT over 2 at 800 K theoretically. All thermoelectric properties were “simultaneously” measured from the same nanowires to facilitate accurate ZT measurements. The surface-boundary scattering is prominent when the nanowire diameter is over ∼100 nm, whereas alloying plays a more important role in suppressing phonon transport for smaller ones.