A model of electrical conduction in polycrystalline silicon

This paper presents a modified version of the conduction model for polycrystalline silicon which includes the thermionic field emission of carriers through the space-charge potential barrier, carrier tunneling through the grain-boundary rectangular potential barrier after being thermally emitted over the space-charge barriers, and the thermionic emission of carriers over these barriers. It is found that if the height of the space-charge potential barrier is much smaller than the height of the grain-boundary barrier, the conduction is mainly controlled by the second mechanism. As grain size decreases, the contribution to current by second mechanism increases. The model predicts that the grain-boundary width in phosphorus-doped polycrystalline silicon film is a strong function of dopant concentration at intermediate dopant concentrations, while the grain-boundary width in boron-doped polycrystalline silicon is independent of dopant concentration in the range of 10¹⁶to 5 × 10¹⁹cm^-3. Considering the potential drop across the grain-boundary barriers, the computed variation of resistivity with dopant concentration for different grain sizes is found to agree with the available experimental data.