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1 Development of High-efficiency Thermoelectric Devices Using Nanowires Jong Wook Roh and Woo Young Lee Department of Materials Science and Engineering, Yonsei University (,,,, ). (thermoelectric effect) Seebeck (1821 ) Peltier (1843 ).( 1 ) (energy consumption) (energy generation),,,.,,, IT, BT.( 2) 1. (a) Seebeck (b) Peltier 33

2 2. 10%,, T. J. Seebeck, Abram Ioffe Seebeck 100 4%. (thermoelectric figure of merit, ZT m ). S Seebeck, (electrical conductivity), k (thermal 3. (Ref.[5]) conductivity). (parameter) (carrier concentration).., 1950 Bi 2 Te 3 (ZT m 1) 2000.( 3) 1993 MIT Dresselhaus power factor(s 2 ) 4 1,2). Dresselhaus (quantum confinement effect), power factor (phonon) (scattering source) Seebeck,.( 5) 2001 RTI(Research 34

3 .. Bi n-type Bi (Ref.[6, 7]) 5. (a) (b) Triangle Institute, ) Venkatasubramanian Bi 2 Te 3 /Sb 2 Te 3 ZT m =2.4 (T m =300K) 3), MIT Harman PbSeTe ) Dresselhaus power factor (heat carrier), (1) MIT Dresselhaus, (2 ) (1 )., 2000 NASA,,, (DOE: Department of Energy) 3, MIT, Caltech, U.C. Berkeley. Bi. 8) MIT Dresselhaus 1993 Bi. Dresselhaus semiclassical transport model band structure model 10nm Bi. 6) (pressure injection method) Bi, 65nm Bi - (semimetal to semiconductor 35

4 transition). 9,10) Bi, Bi Bi array 2 Bi.( 6) 2006 Caltech Heath Bi Seebeck suspended device 72nm Bi Seebeck 25 V/K. Bi Seebeck Bi(Seebeck : 50~100 V/K), - (semimetal-tosemiconductor transition). 11) Si, (ZT m =0.01) Berkeley Yang Caltech Heath Nature Si. Si,. Caltech Heath Si 200K 1. 12) Berkeley 6. Dresselhaus (MIT) (a) Bi array (b) Bi array (Ref. [9]) 7. (a) Heath polycrystalline Bi (b) Seebeck (Ref.[11]) 36

5 . core/shell. Li 10 (a) Te/Bi 2 Te 3 core/shell two-step solution phase 8. Yang (U. C. Berkeley) rough surface Si (a) TEM (b) Si (c) TEM (d), Te/Bi 2 Te 3 core/shell bulk composite., 0.55W/ m-k. 14) 2003 Berkeley Majumdar Si/SiGe microsuspended device, phonon alloy scattering. 15) 9. Si (Ref.[12]) Yang rough surface Si, 0.8W/m-K Si 100,. 13) Yang Si (nano-ribbon), phonon 300K Yang rough Si Si 10. (a) Te/Bi 2 Te 3 core/shell TEM (b) Te/Bi 2 Te 3 core/shell Seebeck 37

6 (2) (ZT~0.8),, LG,. In 4 Se 3-705K 1.48 KIST,, Bi 2 Te ) ETRI top-down 50nm n-type Si - 118µV/K Seebeck. 1,. Bi Bi Bi. 10) Si/SiO 2 Bi Bi (thermodynamic driving force) Bi. Bi aspect ratio.( 11) 120nm Bi 76900cm 2 /Vs, 1.35 m. 17,18) (stress-induced method) whisker,. 19,20) Bi 2 Te 3 compound semiconductor. 21) Bi (nano particles), 11. (a) Bi (b) Bi (c) Bi 38

7 Bi 50.. array,. Bi suspended micro-device Bi Seebeck. 13 (a) suspended micro- 12. Bi suspended micro-device (a) (b) (c) Bi 13. Seebeck (a) (b) 39

8 14. (a) All-in-one MEMS (b) All-in-one MEMS device. 22,23) suspended micro-device SiN x heater Bi, sensing coil (thermal conductance). membrane (thermal resistance) dual-beam Focused ion beam thermal contact 13 (b). Bi 23,24), 98nm Bi 0.8W/m-K Bi( : 8W/m-K) 10. Seebeck Seebeck. 25) 14 (a) Bi Seebeck. micro heater Joule heat (thermal gradient), 4 (4-pointelectrode). 120nm Bi Seebeck 70 V/K, Bi Seebeck. Seebeck. Allin-one MEMS(micro-electromechanical systems), Seebeck. 14 All-in-one MEMS Seebeck, suspended structure, 4. MEMS 4 thermal contact ohmic contact plasma etching. All-in-one MEMS membrane, plasma etching Bi. thermal contact ohmic contact 40

9 , Seebeck., array.. p-type n-type. (parylene),., (glass transition temperature) ,.,,,.,.,, ( ). 41

10 1. Hicks, L.D. and M.S. Dresselhaus, Thermoelectric figure of merit of a one-dimensional conductor. Physical Review B, (24): p Hicks, L.D. and M.S. Dresselhaus, Effect of quantum-well structures on the thermoelectric figure of merit. Physical Review B, (19): p Venkatasubramanian, R., et al., MOCVD of Bi2Te3, Sb2Te3 and their superlattice structures for thin-film thermoelectric applications. Journal of Crystal Growth, (1-4): p Harman, T.C., et al., Quantum dot superlattice thermoelectric materials and devices. Science, (5590): p Majumdar, A., Thermoelectricity in semiconductor nanostructures. Science, (5659): p Lin, Y.M., X.Z. Sun, and M.S. Dresselhaus, Theoretical investigation of thermoelectric transport properties of cylindrical Bi nanowires. Physical Review B, (7): p Dresselhaus, M.S., et al., The promise of lowdimensional thermoelectric materials. Microscale Thermophysical Engineering, (2): p Gallo, C.F., B.S. Chandrasekhar, and P.H. Sutter, Transport Properties of Bismuth Single Crystals. Journal of Applied Physics, (1): p Lin, Y.M., et al., Transport properties of Bi nanowire arrays. Applied Physics Letters, (26): p Zhang, Z.B., et al., Electronic transport properties of single-crystal bismuth nanowire arrays. Physical Review B, (7): p Boukai, A., K. Xu, and J.R. Heath, Size-Dependent Transport and Thermoelectric Properties of Individual Polycrystalline Bismuth Nanowires. Advanced Materials, (7): p Boukai, A.I., et al., Silicon nanowires as efficient thermoelectric materials. Nature, (7175): p Hochbaum, A.I., et al., Enhanced thermoelectric performance of rough silicon nanowires. Nature, (7175): p. 163-U Zhang, G.Q., W. Wang, and X.G. Li, Enhanced Thermoelectric Properties of Core/Shell Heterostructure Nanowire Composites. Advanced Materials, (19): p Li, D.Y., et al., Thermal conductivity of Si/SiGe superlattice nanowires. Applied Physics Letters, (15): p Rhyee, J., et al., Peierls distortion as a route to high themoelectric perdormance in In 4 Se 3-δ Crystal Nature, (18): P Shim, W., et al., On-Film Formation of Bi Nanowires with Extraordinary Electron Mobility. Nano Letters, (1): p Shim, W., et al., Shubnikov--de Haas oscillations in an individual single-crystalline bismuth nanowire grown by on-film formation of nanowires. Applied Physics Letters, (23): p Ham, J., et al., Self-assembled Bi interconnections produced by on-film formation of nanowires for in situ device fabrication. Nanotechnology, (16). 20. Lee, S., et al., Direct observation of the semimetalto-semiconductor transition of individual singlecrystal bismuth nanowires grown by on-film formation of nanowires. Nanotechnology,

11 21(40). 21. Ham, J., et al., Direct Growth of Compound Semiconductor Nanowires by On-Film Formation of Nanowires: Bismuth Telluride. Nano Letters, (8): p Roh, J.W., et al., Size-dependent thermal conductivity of individual single-crystalline PbTe nanowires. Applied Physics Letters, (10): p Li, D.Y., et al., Thermal conductivity of individual silicon nanowires. Applied Physics Letters, (14): p Li, W.X., et al., Phonon transport and thermal conductivity in dielectric quantum wire. Journal of Physics D-Applied Physics, (23): p Jang, S.Y., et al., Transport properties of singlecrystalline n-type semiconducting PbTe nanowires. Nanotechnology, (41). 43

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