Effects of potential barrier height and its fluctuations at grain boundaries on thermoelectric properties of polycrystalline semiconductors

• Published in: Journal of applied physics 2013-08, Vol.114 (5)
• Main Author: Kajikawa, Y.
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.4817243

We study theoretically the effects of grain-boundary potential barriers and their fluctuations in height on the electrical conductivity and the Seebeck coefficient of polycrystalline semiconductors. On the basis of an energy-filtering model, we first derive analytical expressions of the electrical conductivity σ and the Seebeck coefficient α for polycrystalline semiconductors of any degeneracy, assuming grain-boundary potential barriers of a uniform height. These expressions in closed form enable us to perform numerical calculations of σ and α for polycrystalline semiconductors having grain-boundary potential barriers of fluctuated heights. The fluctuated barrier model is applied to the reported experimental data on the electrical conductivity and the Seebeck coefficient of a boron-doped polysilicon sample. Then, the expected enhancement of the thermoelectric power factor due to the energy-filtering effect by the grain-boundary barriers is presented with the mean value and the standard deviation of the potential barrier height as variable parameters. The calculated results suggest that diminishing the fluctuations of the potential barrier height is the key issue for enhancing the power factor by energy filtering.