Band-tail parameter in polysilicon materials

Abstract

We develop a band-tail model in polysilicon by analyzing the energy band structure on the basis of the band-tail parameter with Urbach exponential behavior due to the trap states and the strain in grain bulks and grain boundaries. A quantitative analytical formulation for the band-tail parameter E0 has been deduced by taking into account the carrier–impurity interaction, the carrier–phonon interaction, and the structural disorder. The dependence of E0 and the electric field F in the grain boundary of polysilicon on carrier concentration n0 and temperature T has been studied within the framework of the model. The results indicate that E0 and F increase with T. Furthermore, the increase in E0 at n0=1.0×1018 cm−3 is much larger than that in E0 at n0=1.0×1016 cm−3 at the same temperature. We have demonstrated that the theoretical results are consistent with the experiment, and our model is therefore valuable for both describing polysilicon materials and improving the performance of polysilicon devices.