Thermoelectric properties of nanocrystalline silicon film grown by PECVD

Abstract

We investigate the thermoelectric properties of boron-doped nanocrystalline silicon (nc-Si) films grown by plasma-enhanced chemical-vapor deposition (PECVD). The as-grown nc-Si films with thicknesses of 212 nm were boron-ion implanted to a concentration of 9$\times$10$^{20}$ atoms/cm$^{3}$. Subsequent rapid thermal annealing at 800$^{\circ }$C activated the dopants. X-ray diffraction, Raman spectroscopy and transmission electron microscopy have been employed for structural characterizations. The in-plane electrical conductivity ($\sigma$), and the Seebeck coefficient ( S ) of the doped and annealed film, and the cross-plane thermal conductivity ($\kappa$) of an undoped, but annealed films are measured in the range of 300 K to 750 K. We estimate that the power factor ($\sigma S^{2}$) and the dimensionless figure-of-merit ZT ($\sigma S^{2}$T/$\kappa$) are about 0.50 mW/mK$^{2}$ and 0.11 at 300 K, respectively. These parameters increase with temperature and they are 1.41 mW/mK$^{2}$ and 0.82 at 750 K. The enhancement of ZT is a result of an increase of Seebeck coefficient and a decrease of thermal conductivity caused by a successful reduction of grain sizes of nc-Si films. Our results suggest that heavily ion-implanted nc-Si films provide a new route to realize practical high temperature thin film thermoelectric materials.

Graphical abstract