Band-tail parameter in polysilicon materials

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 E-0 has been deduced by taking into account the carrier-impurity interaction, the carrier-phonon interaction, and the structural disorder. The dependence of E-0 and the electric field F in the grain boundary of polysilicon on carrier concentration n(0) and temperature T has been studied within the framework of the model. The results indicate that E-0 and F increase with T. Furthermore, the increase in E-0 at n(0)=1.0x10(18) cm(-3) is much larger than that in E-0 at n(0)=1.0x10(16) 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. (C) 2001 American Institute of Physics.