Enhanced thermoelectric figure of merit of individual Si nanowires with ultralow contact resistances

Abstract

Low-dimensional silicon-based materials have shown a great potential for thermoelectric applications due to their enhanced figure of merit ZT and high technology compatibility. However, their implementation in real devices remains highly challenging due to the associated large contact resistances (thermal and electrical). Herein we demonstrate ultralow contact resistance silicon nanowires epitaxially grown on scalable devices with enhanced ZT. Temperature dependent figure of merit was fully determined for monolithically integrated individual silicon nanowires achieving a maximum value of ZT = 0.2 at 620 K. Sidewise, this work accounts for the first time nearly zero thermal and electrical contact resistances in monolithically integrated bottom-up nanowires.

High Power Thermoelectric Generator Based on Vertical Silicon Nanowires

“…The most relevant point is the very low thermal conductivity of our SiNW forests, which is 1.8 ± 0.3 W/m K. Several works reported a low thermal conductivity, measured on single silicon nanowires. 8 , 13 , 25 , 40 , 41 In particular, nanowires fabricated by the top-down approach and smoothed by thermal oxidation showed a thermal conductivity over 10 W/(m K). 10 A thermal conductivity smaller than 10 W/(m K) has been measured on vertical nanowire arrays fabricated by lithography and DRIE 22 , 23 , 42 (9 W/(m K), 23 7.5 W/(m K), 22 and 10.1 W(m K) 42 ).…”

“… 42 Alternatively, both VLS and MACE processes can produce large amounts of nanowires without expensive high resolution lithography. VLS produces SiNW with enhanced thermoelectric properties (good Seebeck coefficient and electrical conductivity), with thermal conductivities around 20 W/(m K), 13 , 14 18 W/(m K), 13 and 22 W/(m K) 25 . The thermal conductivity of SiNW produced by MACE, measured on a single nanowire, 11 , 24 , 41 resulted in being smaller than that of VLS nanowires and comprised between 4 and 5 W/(m K).…”

“…The potentialities of silicon as a thermoelectric material have been assessed with devices based on one (or very few) nanowires. 11 , 13 , 14 However, the crucial point to be addressed for practical thermoelectric applications of silicon is to combine large amounts of nanostructures with suitable electrical and thermal connections, so that macroscopic thermoelectric generators (TEGs) capable of delivering enough electrical power can be produced. Large collections of silicon nanostructures can be achieved by bottom-up approaches, based on chemical-vapor deposition (CVD) through the vapor liquid solid (VLS) mechanism.…”

Si and SiGe Nanowire for Micro-Thermoelectric Generator: A Review of the Current State of the Art

“…But it is noteworthy that for different temperatures, the ZT varies widely; the most valuable temperature is 300 K, which is the device's normal operate temperature. For Si, ZT = 0.2 is achieved at 620 K with the optimized contact in a recent work (Gadea Díez et al, 2020).…”

Seebeck coefficient of silicon nanowire forests doped by thermal diffusion

“…However, a large-scale application of thermoelectric devices requires the development of materials that have good thermoelectric features and are, at the same time, of low cost, technologically affordable and sustainable. Silicon has a very high power factor S 2 σ [1][2][3][4] (S is the Seebeck coefficient and σ is the electrical conductivity). This, combined with the reduced thermal conductivity when nanostructured [5][6][7][8][9][10], makes it very suitable for thermoelectric applications.…”