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Graduate Student Seminar - 10/22/2010

"Thermoelectric Figure of Merit Calculations for InSb Nanowires"

by Jane Cornett

Friday, October 22, 2010 -- 12:00 p.m.
Large Conference Room, 1207 Energy Research Facility

Advisor:  Assistant Professor Oded Rabin

By confining a material to a one-dimensional nanowire, the resulting discretization of the density of states function and decreased lattice thermal conductivity due to increased phonon scattering leads to an increase in the thermoelectric figure of merit (ZT). In 1993, Hicks and Dresselhaus reported ZT calculations for one-dimensional Bi2Te3 assuming a one-subband model [1]. Here, we have developed a simplified model for calculating transport properties as a function of nanowire radius for a more realistic multiple-subband system. This method, which can be applied to any single-carrier materials system, is based on a count of the number of subbands contributing to transport and requires little more than calculated electron occupancies of subbands above and below the Fermi energy.

We have applied this model, which approximates the thermoelectric power factor sS2 (where s is the electrical conductivity and S the Seebeck coefficient) as the product of the single-subband power factor value and the maximum Number of Nearly-Degenerate Subbands (NNDS) to room temperature n-type indium antimonide nanowires. For comparison, we also report calculations done assuming the full electronic band structure and find excellent agreement between the two models. Surprisingly, the power factor increases between the radii of 17 and 100 nm due to the substantial increase in degeneracy of subbands with wire radius. We recover the expected monotonic increasing ZT with confinement assuming a radius-dependent lattice thermal conductivity.

1. Hicks, L.D. and Dresselhaus, M.S., Thermoelectric figure of merit of a one-dimensional conductor. Phys. Rev. B, 1993, 47 (24), 16631-16634.

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