Figure-of-merit and emissivity measurement of fine-grained polycrystalline silicon thin films

The thermoelectric properties of phosphorus and boron doped fine-grained polycrystalline silicon thin films have been measured along with the emissivity at room temperature. The thermal conductivity of the films is reduced by one order of magnitude, compared to the undoped single crystalline material, whatever the doping level and the doping atoms are. The electrical conductivity is reduced by the fine-grained structure of the layer, but to a lesser extent than the thermal conductivity. The thermopower remains almost unchanged. As a consequence, the figure-of-merit of these thin films is larger than that of the bulk materials doped at similar carrier concentrations. These measurements suggest that grain size reduction can be effective in enhancing ZT. A link is made between the deposition parameters, the microstructure, and the transport properties.