High thermoelectric figure-of-merits from large-area porous silicon nanowire arrays

High-density and large-area vertically aligned porous silicon nanowire arrays (SiNWAs) with different morphologies, such as various lengths, porosities and heterogeneous diameters, have been successfully fabricated on the two sides of silicon substrate using a simple metal-assisted chemical etching method. The porosity of the nanowires can be controlled by extending the etching time, and the surface area of the porous nanowires can reach as high as 547 m(2) g(-1). The thermoelectric properties of the SINWA/Si/SiNWA sandwich structured composites (SSCs) were measured at room temperature and the figure-of-merit ZT for the corresponding porous SiNWAs were obtained. The results demonstrate that the ZT value of the SSC increases with the increasing porosity of SiNWA, and the porous SiNWAs with the highest surface area exhibit a high Seebeck coefficient up to 513 mu V K-1 and a thermal conductivity down to 1.68 W m(-1) K-1, resulting in a high ZT value of 0.493 at 300 K, which is 77 times higher than that of the bulk silicon (0.0064) and superior to all other reported results for SiNWAs system in terms of thermoelectric properties. The tremendously improved thermoelectric performance coupled with a scalable synthesis indicates the porous SINWAs to be a greatly advanced candidate for the application in high-performance thermoelectric devices. (C) 2015 Elsevier Ltd. All rights reserved.