G. Yuan^1,2, R. Mitdank¹, A. Mogilatenko³, and S.F. Fischer¹

Published in:

J. Phys. Chem. C, vol. 116, no. 25, pp. 13767-13773 (2012).

Abstract:

We report the morphology evolution of porous silicon nanostructures and thermoelectric characterization of silicon nanowires (SiNWs) of Electro-Less Etched (ELE) black silicon. Along the axial direction of NWs, the nanopore density (porosity) increases gradually for both highly doped n-Si (n⁺-Si) and highly doped p-Si (p⁺-Si). The porosity of silicon nanostructures has been demonstrated to be determined mostly by the wafer doping level and etching time. The formation of porous n⁺-SiNWs and porous n⁺⁺-Si film can be understood by an enhanced electron tunnelling from the silicon to the electrolyte through a narrowed space charge layer, while the porous p⁺-SiNW formation could be the result of an increased thermionic emission current over a lower barrier due to a lower band bending. With microfabricated heaters and thermometers, we measured simultaneously electrical resistivity and thermoelectric power (TEP) of boron-doped SiNWs prepared from a Si wafer with resistivity of 0.2-0.4 &Ohm; cm. The electrical conductivity of NWs indicates an increased role of conducting surface states in the ELE SiNWs with a negligible role of surface scattering. The TEP values of NWs at room temperature are around 1.2 ± 0.1 mV/K, which is comparable to the values of bulk silicon for a similar range of dopant concentration.

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