Silicon nanowire arrays for thermoelectric power harvesting

Abstract

Numerous types of thermoelectric materials with best thermoelectric performances have been explored such as bismuth-telluride (Bi2Te3), which is the most commonly found in the market, has a figure-of-merit close to one. However, due to limited sources, highly toxic and expensive, the application of one-dimensional nanomaterial is proposed in thermoelectric micro-energy harvesting, which has been predicted to show improvement in thermoelectric properties. Use of Silicon Nanowire Arrays (SiNWA) as thermoelectric material was reported to reduce thermal conductivity, κ, by a hundredfold compared to bulk Silicon (Si). The properties such as heat flow, temperature difference, ΔT between hot and cold junctions and Seebeck voltage, Voc were evaluated concurrently for different lengths of p- and n-type SiNWA. This thesis reports the performance of SiNWA with two different lengths, 30 μm and 50 μm, on both p- and n-type Si for thermoelectric energy harvesting, and followed by comparing the recorded performance to its bulk Si. A simple and cost-effective technique, metal-assisted chemical etching (MACE), was used to fabricate SiNWA and the nanowires lengths were characterized. An increase in thermal resistance reduces κ for Si, which is advantageous for a thermoelectric material. In this work, heat flow was noticeably decreased in SiNWA samples, resulting in a higher ΔT and Voc than in bulk Si. A larger ΔT between junctions is also attainable in SiNWA by increasing nanowires length. The results have shown that both p- and n-type SiNWA samples (50 μm) have achieved 95 % and 96 % increases in ΔT, respectively, relative to bulk Si samples. In addition, as the length of nanowires increased, a longer time was required to reach a steady value of ΔT. The reduction on approximation values of κ by a hundred-fold which increases thermal resistance as well as Seebeck coefficient, S in the SiNWA samples. Improvement in SiNWA thermoelectric properties will expands the application of SiNWA thermoelectric micro-energy harvesters in various fields such as bio-medical, telecommunication, wireless technologies and others.