Silicon nanowire arrays thermoelectric power harvester

This study aims to investigate the performance of Silicon Nanowire Arrays (SiNWAs) and bulk Si material as thermoelectric power harvesters. SiNWAs were developed using a two-step metal-assisted chemical etching technique. The fabricated thermoelectric devices of 1 × 1 cm p- and n-type SiNWAs each have a diameter of 70–100 nm, and an approximate nanowire length of 6 μm. Bulk Si devices were also tested as a benchmark for the SiNWAs thermoelectric devices. The heat flow across the SiNWAs devices exhibits a higher temperature difference, ΔT, between hot and cold junctions, compared to bulk silicon devices. This reveals that the heat capacity, C, of silicon is reduced significantly by the presence of nanowires. Consequently, a reduction in C also reduces the thermal conductivity of silicon, which is favourable for a good thermoelectric material. Compared to bulk silicon, SiNWAs thermoelectric devices also demonstrate higher Seebeck voltage, Voc, and Seebeck coefficient, S. The voltage rises as the ΔT between two junctions increases. An increase in Voc and S in the SiNWAs thermoelectric device aids to improve the figure-of-merit and the efficiency of the thermoelectric device. Experimental characterization of all fabricated thermoelectric devices suggest that the p-SiNWAs device possesses the highest ΔT of 17°C at 40 sec; Voc = ∼35 mV and S = ∼8 mV/K.