High thermoelectric figure of merit in silicon nanowire via corrugated surfaces

Abstract

The energy crisis presents a significant danger to impede the efforts towards environmental preservation and the achievement of sustainable development. To overcome problems, various renewable energy technologies, such as solar cells and wind power generation, have been developed, and thermoelectric generation is under development as a new energy alternative [1, 2]. The thermoelectric device is one of the ideal future renewable energy technologies since the heat can directly convert into electricity, enabling energy harvesting without mechanical noise, vibration, or moving parts. However, the energy conversion efficiency of thermoelectric systems is generally low, making application difficult [3]. Thus, various nano-based thermoelectric devices have been proposed as candidates with improved figure of merit (ZT) [4, 5]. Among them, silicon-based thermoelectric devices have been an attractive candidate because it is possible to increase ZT through lower thermal conductivity according to decrease in diameter of nanowire (DNW) [6, 7]. However, it also has a problem, like still a low ZT. In this study, we suggest silicon nanowires with corrugated surfaces (CSiNWs) using Bosch process of deep reactive ion etcher (DRIE) [8]. CSiNWs produce much more phonon backscattering due to the geometry of asperity, which can lead to strong suppression of the phonon mean free path (MFP). In addition, since there are many corrugated surfaces formed on the surface, multiple scattering can also be generated. Therefore, the к can be further reduced by more than two times compared to the previously reported silicon nanowire with rough surface. As a result, Boron- (DNW: 191 nm) and Phosphorus-doped CSiNW (DNW: 173 nm) show lowest к of 4.9±0.56 and 6.1±0.7 W·m-1·K-1, and a high ZT of 0.345 has been achieved with appropriate doping concentration in n-type.