Thermoelectric properties of nanocrystalline silicon film grown by PECVD

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 × 10 ^20 atoms/cm ^3 . Subsequent rapid thermal annealing at 800 ^∘ C activated the dopants. X-ray diffraction, Raman spectroscopy and transmission electron microscopy have been employed for structural characterizations. The in-plane electrical conductivity ( σ ), and the Seebeck coefficient ( S ) of the doped and annealed film, and the cross-plane thermal conductivity ( κ ) of an undoped, but annealed films are measured in the range of 300 K to 750 K. We estimate that the power factor ( σ S^2 ) and the dimensionless figure-of-merit ZT ( σ S^2 T/ κ ) 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