Modeling thermoelectric properties of TI materials: a Landauer approach Jesse Maassen and Mark Lundstrom Network for Computational Nanotechnology, Electrical and Computer Engineering, Purdue University, West Lafayette, IN USA DARPA-TI meeting, April 25, 2012
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Modeling thermoelectric properties of TI materials: a Landauer approach Jesse Maassen and Mark Lundstrom Network for Computational Nanotechnology, Electrical.
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Modeling thermoelectric properties of TI materials:
a Landauer approach
Jesse Maassen and Mark Lundstrom
Network for Computational Nanotechnology,Electrical and Computer Engineering,
Purdue University,West Lafayette, IN USA
DARPA-TI meeting, April 25, 2012
Overview
• Motivation.
• Summary of the thermoelectric effect.
• Thermoelectric modeling within the Landauer approach.
• Example: effect of TI surface states on the thermoelectric properties of Bi2Te3 films.
Motivation• In recent years, much research has focused energy-related science and technology,
in particular thermoelectrics.
• Some of the best known thermoelectric materials happen to be topological insulators (e.g., Bi2Te3).
• Work has appeared showing that TI surface states in ultra-thin films (<10 nm) can lead to enhanced thermoelectric properties.
ZT ~ 2P. Ghaemi et al., Phys. Rev. Lett. 105, 166603 (2010).
ZT ~ 7F. Zahid and R. Lake, Appl. Phys. Lett. 97, 212102 (2010).
Next step is to reproduce and perhaps expand these results.
• Decreasing λsurf one order of magnitude is equivalent to increasing tfilm by the same factor.
tfilm = 10 nm tfilm = 100 nm
Power factor (TI + bulk states)
• Significant reduction in power factor with the presence of TI surface states.
• Aside from conductivity, all thermoelectric characteristics are degraded with the surface states.
• Hinder surface conduction by enhancing scattering or destroying the surface states.
Surface roughness or adding magnetic impurities may enhance thermoelectric performance.
€
ZT =S2σ T
κ e + κ l
Conclusions
• Landauer approach is a powerful formalism for calculating the thermoelectric coefficients of materials, particularly when combined with full band descriptions of electronic dispersion.
• This method naturally spans from ballistic to diffusive transport regimes and considers bulk and nano-scale systems.
• Within our example, TI surface states were shown to degrade the thermoelectric performance of Bi2Te3 films (when the thickness is large enough to
form a gap in the TI states).
• Hindering surface conduction may enhance thermoelectric performance, e.g. introducing surface roughness and/or magnetic impurities.