Letter

Nature 451, 168-171 (10 January 2008) | doi:10.1038/nature06458; Received 15 June 2007; Accepted 2 November 2007

Silicon nanowires as efficient thermoelectric materials

Akram I. Boukai1,2, Yuri Bunimovich1,2, Jamil Tahir-Kheli1, Jen-Kan Yu1, William A. Goddard III1 & James R. Heath1

  1. Division of Chemistry and Chemical Engineering, MC 127-72, 1200 East California Blvd, California Institute of Technology, Pasadena, California 91125, USA
  2. These authors contributed equally to this work.

Correspondence to: James R. Heath1 Correspondence and requests for materials should be addressed to J.R.H. (Email: heath@caltech.edu).

Thermoelectric materials interconvert thermal gradients and electric fields for power generation or for refrigeration1, 2. Thermoelectrics currently find only niche applications because of their limited efficiency, which is measured by the dimensionless parameter ZT—a function of the Seebeck coefficient or thermoelectric power, and of the electrical and thermal conductivities. Maximizing ZT is challenging because optimizing one physical parameter often adversely affects another3. Several groups have achieved significant improvements in ZT through multi-component nanostructured thermoelectrics4, 5, 6, such as Bi2Te3/Sb2Te3 thin-film superlattices, or embedded PbSeTe quantum dot superlattices. Here we report efficient thermoelectric performance from the single-component system of silicon nanowires for cross-sectional areas of 10 nm times 20 nm and 20 nm times 20 nm. By varying the nanowire size and impurity doping levels, ZT values representing an approximately 100-fold improvement over bulk Si are achieved over a broad temperature range, including ZT approximately 1 at 200 K. Independent measurements of the Seebeck coefficient, the electrical conductivity and the thermal conductivity, combined with theory, indicate that the improved efficiency originates from phonon effects. These results are expected to apply to other classes of semiconductor nanomaterials.

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