Porous Nanostructures and Thermoelectric Power Measurement of Electro-Less Etched Black Silicon

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 Ω cm. The electrical conduc...